The rare stone fact bank

Every fact the six books state, with who it is true of, how sure the science is, and where it comes from: 56 facts and 31 sources.

Showing all 56 facts

How it formsEstablished

Some gem crystals are found where they grew, inside rock.

Gem corundum deposits are classed as primary or secondary. Gems & Gemology (2019) says primary corundum deposits hold the gem in the rock where it crystallized (or in a rock that carried it up), while secondary deposits, present-day placers, result from the erosion of primary deposits. Red beryl is a worked example: in Utah's Wah Wah Mountains it is found along fractures in the rhyolite where it crystallized (Utah Geological Survey). Some, not all: a gem in a secondary deposit is no longer in the rock where it grew.

True of
gem minerals in their host rock (primary deposits)
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some
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2 sources
  1. Gemological Institute of America Geology of Corundum and Emerald Gem Deposits: A Review (Gems & Gemology, Winter 2019) journal, 2019
  2. Utah Geological Survey Glad You Asked: What gemstone is found in Utah that is rarer than diamond and more valuable than gold? government, 2002
How it formsEstablished

Gem red beryl grew in cracks in rhyolite, a volcanic rock, in Utah's Wah Wah Mountains.

Gems & Gemology (2003) says red beryl at the Ruby Violet mine is found mostly along fractures, often clay-filled, in a topaz rhyolite, and that it crystallized there as a vapor-phase mineral from rhyolite-derived gases, heated ground-water vapors and the rock's own minerals and glass. The Utah Geological Survey describes the Wah Wah crystals along near-vertical fractures and clay-filled seams in rhyolite that erupted from volcanic vents about 18 to 20 million years ago. Red beryl from Utah's Thomas Range also occurs in rhyolite cavities, but those crystals are mostly too small to cut.

True of
gem-quality red beryl from the Wah Wah Mountains, Utah
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2 sources
  1. Gemological Institute of America Red Beryl from Utah: A Review and Update (Gems & Gemology, Winter 2003) journal, 2003
  2. Utah Geological Survey Glad You Asked: What gemstone is found in Utah that is rarer than diamond and more valuable than gold? government, 2002
How it formsEstablished

At the Ruby Violet mine, red beryl crystallized from hot gases and vapors in volcanic rhyolite.

Gems & Gemology describes Ruby Violet red beryl as a vapor-phase mineral that crystallized from rhyolite-derived gases, heated ground-water vapors and minerals and glass in the rock. This concerns the Ruby Violet mine's gem-quality red beryl, not every beryl deposit.

True of
gem-quality red beryl at the Ruby Violet mine, Utah
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Used inNot in the books yet
1 source
  1. Gemological Institute of America Red Beryl from Utah: A Review and Update (Gems & Gemology, Winter 2003) journal, 2003
What it's made ofEstablished

Natural kyawthuite is a heavy orange-brown oxide mineral made of bismuth, antimony and oxygen.

Mineralogical Magazine (2017) and EarthDate describe kyawthuite as a reddish-orange to orange-brown bismuth antimony oxide (Bi3+Sb5+O4) with high density.

True of
kyawthuite composition and appearance
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2 sources
  1. Mineralogical Magazine Kyawthuite, Bi3+Sb5+O4, a new gem mineral from Mogok, Burma (Myanmar) journal, 2017
  2. EarthDate (Switch Energy Alliance) Earth’s Rarest Mineral ngo, 2025
Crystal shapeEstablished

The only known kyawthuite is a cut gem that weighs 1.61 carats, about a third of a gram.

The one kyawthuite crystal was faceted into a 1.61-carat gem (Mineralogical Magazine 2017; EarthDate). A carat is 0.2 gram, so 1.61 carats is about 0.32 gram; Wikipedia calls it a 0.3-gram sample. The stone is on display at the Natural History Museum of Los Angeles County. The weight is the cut gem's, not the rough crystal's.

True of
the kyawthuite type specimen
Numbers
  • 1.61 carats (about 0.32 g) weight of the cut gema carat is 0.2 g; Wikipedia rounds it to 0.3 g
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3 sources
  1. Mineralogical Magazine Kyawthuite, Bi3+Sb5+O4, a new gem mineral from Mogok, Burma (Myanmar) journal, 2017
  2. EarthDate (Switch Energy Alliance) Earth’s Rarest Mineral ngo, 2025
  3. Wikipedia Kyawthuite encyclopedia
Crystal shapeEstablished

Painite belongs to the hexagonal crystal system, and its crystals grow long.

The Handbook of Mineralogy gives painite's crystal system as hexagonal and describes elongated crystals up to 1.5 cm. It also calls the crystals pseudo-orthorhombic, and Wikipedia notes they may look orthorhombic, so not every painite crystal shows a clean six-sided outline; hexagonal names the mineral's internal symmetry.

True of
painite crystals
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2 sources
  1. Mineralogical Society of America Handbook of Mineralogy: Painite book
  2. Wikipedia Painite encyclopedia
Crystal shapeEstablished

Unlike spinel, taaffeite splits light into two rays, a crystal property called double refraction that gave away the mystery stone.

Spinel is singly refractive, whereas taaffeite is doubly refractive (uniaxial negative). Geosciences LibreTexts explains that observing weak double refraction in a stone that otherwise matched spinel's properties was the clue that led Taaffe to send the gem for laboratory testing.

True of
taaffeite and spinel optical properties
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2 sources
  1. Geosciences LibreTexts 16.67: Taaffeite university
  2. National Jeweler 5 Things to Know About … Taaffeite news, 2020
Color and glowEstablished

Benitoite glows bright blue under shortwave ultraviolet light.

The Handbook of Mineralogy lists blue fluorescence under shortwave UV for benitoite. Gems & Gemology (1997) found that blue benitoites from California's New Idria district fluoresced strong blue under short-wave UV and were inert under long-wave UV. Shortwave UV lamps can hurt eyes and skin, so the books show the glow in a museum case or as an adult's demonstration.

True of
benitoite under a shortwave ultraviolet lamp
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2 sources
  1. Mineralogical Society of America Handbook of Mineralogy: Benitoite book
  2. Gemological Institute of America Benitoite from the New Idria District, San Benito County, California (Gems & Gemology, Fall 1997) journal, 1997
Color and glowEstablished

Benitoite is also called the "blue diamond" because of its deep transparent blue color.

The California State Capitol Museum says this rare gemstone is also known as the “blue diamond” because of its deep shades of transparent blue color. This is a nickname for benitoite, not a claim that it is diamond.

True of
California State Capitol Museum's benitoite description
Must keep
also
Corrects
Benitoite is a diamond.
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Used inNot in the books yet
1 source
  1. California State Capitol Museum Gemstone – Benitoite government
Color and glowEstablished

Part of painite's orange-red color comes from chromium, the element that makes ruby red.

Wikipedia reports that trace amounts of chromium and vanadium are responsible for painite's typically orange-red to brownish-red color; the Handbook of Mineralogy's analyses list small amounts of both oxides. GIA states that chromium is the trace element that causes ruby's red. Chromium is one cause of painite's color, not the only one, which is why the claim says part.

True of
painite's color (chromium and vanadium both contribute)
Must keep
part
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Used inNot in the books yet
3 sources
  1. Wikipedia Painite encyclopedia
  2. Mineralogical Society of America Handbook of Mineralogy: Painite book
  3. GIA Ruby Description ngo
Color and glowEstablished

Manganese helps give red beryl its red color.

The Utah Geological Survey says red beryl gets its red color from manganese, with smaller amounts of iron, chromium and calcium also present. This is a statement about red beryl's color chemistry, not a rule for every red gem.

True of
red beryl
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1 source
  1. Utah Geological Survey Glad You Asked: What gemstone is found in Utah that is rarer than diamond and more valuable than gold? government, 2002
Color and glowEstablished

Turning a rough tanzanite crystal in the light can show different colors—blue, violet and burgundy—along its three crystal directions.

GIA explains that tanzanite is strongly pleochroic (trichroic): a crystal can show blue, violet-purple and brownish or burgundy hues depending on the viewing direction, so cutters orient each stone carefully.

True of
tanzanite pleochroism
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can
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2 sources
  1. GIA Tanzanite ngo
  2. U.S. Geological Survey The Mineral Industry of Tanzania in 2019 (2019 Minerals Yearbook) government, 2023
Color and glowEstablished

Grandidierite's bluish-green to greenish-blue color comes from iron inside its crystal structure.

The Handbook of Mineralogy and GIA (2015) describe grandidierite as a magnesium aluminum borosilicate whose greenish-blue to bluish-green color increases with its iron (Fe) content.

True of
grandidierite color
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2 sources
  1. Mineralogical Society of America Grandidierite (Handbook of Mineralogy) journal
  2. Gemological Institute of America Transparent Grandidierite from Madagascar (Gems & Gemology, Winter 2015) journal, 2015
Color and glowEstablished

Clear grandidierite is trichroic, showing dark blue-green, colorless and dark green hues as the crystal turns in light.

Both the Handbook of Mineralogy and GIA (2015) document grandidierite's strong trichroism: viewing the crystal along different directions shows deep blue-green, colorless (very pale yellow), and dark green.

True of
grandidierite pleochroism
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2 sources
  1. Mineralogical Society of America Grandidierite (Handbook of Mineralogy) journal
  2. Gemological Institute of America Transparent Grandidierite from Madagascar (Gems & Gemology, Winter 2015) journal, 2015
HardnessEstablished

At 6 to 7 on the Mohs scale, tanzanite is softer than sapphire and can split if knocked hard.

GIA gives tanzanite's Mohs hardness as 6 to 7 (softer than corundum/sapphire at 9) and notes that it has one direction of cleavage, so it requires care against sharp blows.

True of
tanzanite hardness and care
Must keep
can
Numbers
  • 6 to 7 Mohs hardness
Corrects
Tanzanite is a variety of sapphire.
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2 sources
  1. GIA Tanzanite ngo
  2. U.S. Geological Survey The Mineral Industry of Tanzania in 2019 (2019 Minerals Yearbook) government, 2023
HardnessEstablished

With a Mohs hardness of 7.5, grandidierite is a hard borosilicate mineral that formed under intense heat and pressure.

The Handbook of Mineralogy and GIA (2015) report grandidierite's Mohs hardness as 7.5 and describe its formation in aluminous, boron-rich rocks subjected to high-temperature metamorphism.

True of
grandidierite hardness and formation
Numbers
  • 7.5 Mohs hardness
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2 sources
  1. Mineralogical Society of America Grandidierite (Handbook of Mineralogy) journal
  2. Gemological Institute of America Transparent Grandidierite from Madagascar (Gems & Gemology, Winter 2015) journal, 2015
HardnessEstablished

Musgravite is a hard gem at 8 to 8.5 on the Mohs scale, often showing soft olive-green, gray or violet-gray colors.

The Handbook of Mineralogy and GIA (2013) give musgravite's Mohs hardness as 8 to 8.5 and describe its colors as olive-green, greenish gray, grayish violet, or brownish purple.

True of
musgravite hardness and color
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often
Numbers
  • 8 to 8.5 Mohs hardness
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Used inNot in the books yet
2 sources
  1. Gemological Institute of America Musgravite from Myanmar (Gems & Gemology, Spring 2013) journal, 2013
  2. Mineralogical Society of America Magnesiotaaffeite-6N'3S / Musgravite (Handbook of Mineralogy) journal
Where it's foundEstablished

The Ruby Violet mine in Utah's Wah Wah Mountains is the only known commercial source of gem-quality red beryl.

Gems & Gemology (2003) opens: there is only one known commercial occurrence of gem-quality red beryl in the world, the Ruby Violet (or Red Beryl) mine in the Wah Wah Mountains of Beaver County, Utah. The Utah Geological Survey calls the Ruby-Violet claims the only known deposit of large, gem-quality red beryl, and names two other localities, Utah's Thomas Range, where many crystals are too small to facet, and New Mexico's Black Range. The claims are private; no collecting is allowed without the claim owners' permission.

True of
commercial gem-quality red beryl
Must keep
known
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2 sources
  1. Gemological Institute of America Red Beryl from Utah: A Review and Update (Gems & Gemology, Winter 2003) journal, 2003
  2. Utah Geological Survey Glad You Asked: What gemstone is found in Utah that is rarer than diamond and more valuable than gold? government, 2002
Where it's foundEstablished

Tanzanite's only known source is the Merelani Hills near Mount Kilimanjaro in Tanzania.

GIA says tanzanite has only one source, the hills of Merelani in northern Tanzania, near Mount Kilimanjaro, where it was first found in 1967. The USGS Minerals Yearbook for Tanzania (2019) calls Merelani, near Arusha, the world's only source of tanzanite and Tanzania the world's only producer. Only-source statements describe what is known today.

True of
tanzanite deposits
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known
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2 sources
  1. GIA Tanzanite ngo
  2. U.S. Geological Survey The Mineral Industry of Tanzania in 2019 (2019 Minerals Yearbook) government, 2023
Where it's foundEstablished

Tanzanite is mined in just one place, the Merelani Hills of Tanzania.

GIA: tanzanite is commercially mined in only one place, and has only one source, the hills of Merelani in northern Tanzania. The USGS Minerals Yearbook (2019) describes tanzanite mining at Merelani, including the large-scale Block C operation.

True of
tanzanite mining
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2 sources
  1. GIA Tanzanite ngo
  2. U.S. Geological Survey The Mineral Industry of Tanzania in 2019 (2019 Minerals Yearbook) government, 2023
Where it's foundEstablished

Many red beryl crystals from Utah's Thomas Range are too small to cut.

The Utah Geological Survey notes that red beryl occurs at Utah's Thomas Range, but many crystals there are too small to facet. This does not mean every Thomas Range crystal is uncuttable or that every red beryl source is the same.

True of
red beryl crystals from Utah's Thomas Range
Must keep
many
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Used inNot in the books yet
1 source
  1. Utah Geological Survey Glad You Asked: What gemstone is found in Utah that is rarer than diamond and more valuable than gold? government, 2002
Where it's foundEstablished

The Benitoite Gem mine is the only commercial source of gem-quality benitoite in the world.

Gems & Gemology reports that all commercial gem production has come from the Benitoite Gem mine in the New Idria district of San Benito County, California. Benitoite has been confirmed in other locations, but the article distinguishes those from commercial gem-quality production.

True of
commercial gem-quality benitoite
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1 source
  1. Gemological Institute of America Benitoite from the New Idria District, San Benito County, California (Gems & Gemology, Fall 1997) journal, 1997
Where it's foundEstablished

Gem-quality taaffeite has been found in alluvial deposits in Sri Lanka and Tanzania, as well as in sediments in Myanmar.

Geosciences LibreTexts lists Sri Lanka (where most early cut stones originated in alluvial gravels), Tanzania (Tunduru), and Myanmar as documented localities for taaffeite.

True of
documented taaffeite localities
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2 sources
  1. Geosciences LibreTexts 16.67: Taaffeite university
  2. National Jeweler 5 Things to Know About … Taaffeite news, 2020
Where it's foundEstablished

In 2014 miners near Tranomaro in southern Madagascar found pockets of grandidierite that yielded some clear blue-green gems.

GIA (Winter 2015) reports that a deposit discovered in May 2014 near the village of Tranomaro in southern Madagascar's Androy region produced rough grandidierite with rare transparent areas suitable for faceting.

True of
the Tranomaro grandidierite find, Madagascar
Must keep
some
Numbers
  • 2014 year of Tranomaro discovery
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2 sources
  1. Mineralogical Society of America Grandidierite (Handbook of Mineralogy) journal
  2. Gemological Institute of America Transparent Grandidierite from Madagascar (Gems & Gemology, Winter 2015) journal, 2015
Where it's foundEstablished

Small numbers of gem-quality musgravite crystals have been identified from Sri Lanka and from Mogok in Myanmar.

GIA (Spring 2013) and the Handbook of Mineralogy document gem-quality musgravite from Sri Lanka and from Mogok, Myanmar (including a 3.05-carat crystal examined by GIA), as well as occurrences in Madagascar, Greenland, and Antarctica.

True of
gem-quality musgravite localities
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small
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Used inNot in the books yet
2 sources
  1. Gemological Institute of America Musgravite from Myanmar (Gems & Gemology, Spring 2013) journal, 2013
  2. Mineralogical Society of America Magnesiotaaffeite-6N'3S / Musgravite (Handbook of Mineralogy) journal
How rareEstablished

For many years, only two painite crystals were known to science.

Gems & Gemology (Winter 2005) reports that for many years after the early-1950s discovery only two crystals of painite (1.7 and 2.1 g) were known to exist, and that a third crystal was later found in a batch of gem rough at GIA. The third was described in 1986 (Shigley et al., Mineralogical Magazine), cited by Gems & Gemology. The count is historical: the rarity began to change in 2001, and by 2005 more than a thousand crystals and fragments had been recovered. It records what scientists knew about, not how many crystals existed in the ground.

True of
painite crystals documented by scientists between the 1950s find and 1986, when a third was described
Must keep
for many years
Numbers
  • two painite crystals knownfor many years after the early-1950s find, until a third crystal was described in 1986 (Gems & Gemology 2005)
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2 sources
  1. Gemological Institute of America Gem News International: New discoveries of painite in Myanmar (Burma), Gems & Gemology, Winter 2005 journal, 2005
  2. Energy & Geoscience Institute, University of Utah ASK EGI: No Painite, No Gain university, 2026
How rareEstablished

Once, people knew of just two painite crystals.

The plain-words retelling of painite-two-known for early readers. Gems & Gemology (2005) and EGI both report that for many years only two painite crystals were known; the word once keeps it in the past, because more than a thousand crystals and fragments have been recovered since 2001. It is about what people knew, not about how many existed.

True of
painite crystals documented by scientists between the 1950s find and 1986, when a third was described
Must keep
once
Numbers
  • two painite crystals knownfor many years after the early-1950s find, until a third crystal was described in 1986 (Gems & Gemology 2005)
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2 sources
  1. Gemological Institute of America Gem News International: New discoveries of painite in Myanmar (Burma), Gems & Gemology, Winter 2005 journal, 2005
  2. Energy & Geoscience Institute, University of Utah ASK EGI: No Painite, No Gain university, 2026
How rareEstablished

Since the early 2000s, miners in Myanmar have found more than a thousand painite crystals and fragments.

Gems & Gemology (Winter 2005) dates the change to 2001, when an 11 g crystal was found near Mogok; more finds in secondary deposits around Mogok followed in 2004, painite was found in the rock at Thurein-taung and the Wetloo mine in May 2005, and more than a thousand crystals and crystal fragments had been recovered by then. Wikipedia reports several thousand specimens from the Mogok area since.

True of
painite from the Mogok area of Myanmar
Numbers
  • more than a thousand crystals and fragments recovered since 2001Gems & Gemology counted more than a thousand by late 2005; Wikipedia gives several thousand
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2 sources
  1. Gemological Institute of America Gem News International: New discoveries of painite in Myanmar (Burma), Gems & Gemology, Winter 2005 journal, 2005
  2. Wikipedia Painite encyclopedia
How rareEstablished

Only some painite is good enough to cut as a gem, and gem-quality painite is still rare.

Of the painite rough recovered near Mogok by 2005, Gems & Gemology reports that only a small percentage was suitable for faceting, and most cut stones were small (0.05 to 0.30 ct). EGI says gem-quality painite stones are exceptionally rare even after the new discoveries, and that most specimens are fragments. Rare here means rare as cut gems, not that painite crystals are still unknown.

True of
gem-quality (facetable) painite
Must keep
some
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2 sources
  1. Gemological Institute of America Gem News International: New discoveries of painite in Myanmar (Burma), Gems & Gemology, Winter 2005 journal, 2005
  2. Energy & Geoscience Institute, University of Utah ASK EGI: No Painite, No Gain university, 2026
How rareEstablished

Kyawthuite is known from a single crystal, found near Mogok, Myanmar.

Mineralogical Magazine (2017) describes kyawthuite from a waterworn crystal found in alluvium in the Chaung-gyi valley near Mogok, Burma (Myanmar); the description rests on that single sample. EarthDate reports that miners found it in 2010 and that only one specimen has been found. Known means documented: EarthDate itself says more kyawthuite could possibly exist.

True of
kyawthuite specimens documented by scientists
Must keep
known
Numbers
  • one known crystals
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2 sources
  1. Mineralogical Magazine Kyawthuite, Bi3+Sb5+O4, a new gem mineral from Mogok, Burma (Myanmar) journal, 2017
  2. EarthDate (Switch Energy Alliance) Earth’s Rarest Mineral ngo, 2025
How rareEstablished

Scientists have just one kyawthuite crystal to study.

The plain-words retelling of kyawthuite-one-crystal. Mineralogical Magazine (2017) bases the mineral's description on a single sample, and EarthDate notes that with only one small specimen, further study cannot be done without damaging it. It says what scientists have, not that no other crystal exists.

True of
kyawthuite specimens documented by scientists
Must keep
have
Numbers
  • one known crystals
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2 sources
  1. Mineralogical Magazine Kyawthuite, Bi3+Sb5+O4, a new gem mineral from Mogok, Burma (Myanmar) journal, 2017
  2. EarthDate (Switch Energy Alliance) Earth’s Rarest Mineral ngo, 2025
How rareEstablished

Having one documented kyawthuite crystal does not prove no other crystal exists, and more kyawthuite could possibly wait in the ground.

EarthDate explicitly notes that while only one natural kyawthuite specimen has been documented by scientists so far, more specimens could possibly exist undiscovered in Myanmar or elsewhere.

True of
kyawthuite rarity
Must keep
documented
Corrects
Scientists have proved that only one kyawthuite crystal exists anywhere on Earth.
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Used inNot in the books yet
2 sources
  1. Mineralogical Magazine Kyawthuite, Bi3+Sb5+O4, a new gem mineral from Mogok, Burma (Myanmar) journal, 2017
  2. EarthDate (Switch Energy Alliance) Earth’s Rarest Mineral ngo, 2025
How rareEstablished

Most grandidierite crystals are cloudy or translucent, so transparent facet-grade gems are especially scarce.

GIA (Winter 2015) notes that while grandidierite occurs in high-grade metamorphic rocks, most crystals are translucent to opaque with many inclusions; transparent facetable gems remained practically unknown until a 2014 deposit near Tranomaro, Madagascar produced some clear stones.

True of
transparent gem-quality grandidierite
Must keep
most
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Fold 2
Used inNot in the books yet
2 sources
  1. Mineralogical Society of America Grandidierite (Handbook of Mineralogy) journal
  2. Gemological Institute of America Transparent Grandidierite from Madagascar (Gems & Gemology, Winter 2015) journal, 2015
How rareEstablished

Although musgravite was named in 1967, the first faceted gem-quality musgravite was not reported until 1993.

GIA (Spring 2013) notes that after musgravite's initial description as a mineral in 1967, the first facet-grade gemstones were not identified until 1993, and confirmed faceted specimens remain very scarce.

True of
faceted gem-quality musgravite history
Numbers
  • 1993 year first faceted musgravite reported
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Used inNot in the books yet
2 sources
  1. Gemological Institute of America Musgravite from Myanmar (Gems & Gemology, Spring 2013) journal, 2013
  2. Mineralogical Society of America Magnesiotaaffeite-6N'3S / Musgravite (Handbook of Mineralogy) journal
Discovery and namesEstablished

Painite was first found in Myanmar in the early 1950s by gem collector Arthur C. D. Pain.

Gems & Gemology (2005) says painite was discovered in the early 1950s in the vicinity of Mogok, Burma (Myanmar); the University of Utah's EGI places Arthur C. D. Pain's find in the Mogok region in the 1950s. The Handbook of Mineralogy names the mineral for Arthur Charles Davy Pain (1901-1971), a British gem collector who first noted the species, and gives its type locality near Ohngaing village in the Mogok district, where it occurs in gem gravels. The sources say Pain noted or came upon the crystal; none records how he got it out of the ground.

True of
the first painite specimens, Mogok area, Myanmar
Numbers
  • 1950s decade first foundGems & Gemology (2005): the early 1950s, near Mogok
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3 sources
  1. Gemological Institute of America Gem News International: New discoveries of painite in Myanmar (Burma), Gems & Gemology, Winter 2005 journal, 2005
  2. Energy & Geoscience Institute, University of Utah ASK EGI: No Painite, No Gain university, 2026
  3. Mineralogical Society of America Handbook of Mineralogy: Painite book
Discovery and namesEstablished

Benitoite was first discovered in 1907 in California's San Benito Mountains.

The California State Capitol Museum says benitoite was first discovered in 1907 in the San Benito Mountains. GIA likewise places its first discovery in the New Idria district of San Benito County in 1907.

True of
benitoite discovery
Numbers
  • 1907 year first discovered
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Used inNot in the books yet
2 sources
  1. California State Capitol Museum Gemstone – Benitoite government
  2. Gemological Institute of America Benitoite from the New Idria District, San Benito County, California (Gems & Gemology, Fall 1997) journal, 1997
Discovery and namesEstablished

The first known taaffeite was a gem that had already been cut, noticed in 1945 among stones from a Dublin jeweller.

The Geosciences LibreTexts gemology text says Count Edward Charles Richard Taaffe found the stone by chance in October 1945 in a lot of gemstones bought from the Dublin jeweller Robert Dobbie; National Jeweler says that in 1945 Taaffe was sorting a parcel of cut and polished stones and noticed a mauve stone that looked like spinel but was doubly refractive. Both sources call taaffeite the only mineral first identified from a faceted stone; the books keep the modest claim that the first known taaffeite was already cut.

True of
the first taaffeite specimen known
Numbers
  • 1945 year the stone was noticed
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2 sources
  1. Geosciences LibreTexts 16.67: Taaffeite university
  2. National Jeweler 5 Things to Know About … Taaffeite news, 2020
Discovery and namesEstablished

Laboratory tests showed the stone was a mineral no one had described, and it was named taaffeite after Count Edward Taaffe, who noticed it.

Puzzled by a cut stone with spinel-like properties but double refraction, Taaffe sent it to Basil Anderson at the Laboratory of the London Chamber of Commerce, where it was identified as a new mineral species (LibreTexts); National Jeweler adds that part of the stone was used up in the analysis. The mineral was named after Taaffe. Its formal name as a mineral is now magnesiotaaffeite-2N'2S.

True of
the first taaffeite specimen
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2 sources
  1. Geosciences LibreTexts 16.67: Taaffeite university
  2. National Jeweler 5 Things to Know About … Taaffeite news, 2020
Discovery and namesEstablished

Tanzanite was first found in 1967 in the Merelani Hills of northern Tanzania, near Mount Kilimanjaro.

GIA and the USGS Minerals Yearbook report that transparent blue-violet zoisite crystals were discovered in the Merelani Hills near Arusha and Mount Kilimanjaro in northern Tanzania in 1967, and named tanzanite after their country of origin.

True of
tanzanite discovery
Numbers
  • 1967 year of discovery
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Used inNot in the books yet
2 sources
  1. GIA Tanzanite ngo
  2. U.S. Geological Survey The Mineral Industry of Tanzania in 2019 (2019 Minerals Yearbook) government, 2023
Discovery and namesEstablished

A UC Berkeley mineralogist named benitoite after the place where it was discovered.

The California State Capitol Museum says that two years after the 1907 discovery, a UC Berkeley mineralogist gave the gemstone the label benitoite after its discovery place. GIA reports that it was named after San Benito County, the San Benito River and nearby San Benito Mountain.

True of
benitoite name
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Used inNot in the books yet
2 sources
  1. California State Capitol Museum Gemstone – Benitoite government
  2. Gemological Institute of America Benitoite from the New Idria District, San Benito County, California (Gems & Gemology, Fall 1997) journal, 1997
Discovery and namesEstablished

The known kyawthuite crystal was found in stream gravel in the Chaung-gyi valley near Mogok, Myanmar, and named for mineralogist Kyaw Thu.

Mineralogical Magazine (2017) reports that the single waterworn crystal was recovered from alluvium in the Chaung-gyi valley near Mogok, Myanmar, and named in honour of Burmese mineralogist and gemologist Dr. Kyaw Thu.

True of
the kyawthuite type specimen
Must keep
known
First fold
Fold 2
Used inNot in the books yet
2 sources
  1. Mineralogical Magazine Kyawthuite, Bi3+Sb5+O4, a new gem mineral from Mogok, Burma (Myanmar) journal, 2017
  2. EarthDate (Switch Energy Alliance) Earth’s Rarest Mineral ngo, 2025
Discovery and namesEstablished

Grandidierite was first described in 1902 from cliffs at Andrahomana in southern Madagascar and named for naturalist Alfred Grandidier.

The Handbook of Mineralogy and GIA report that French mineralogist Alfred Lacroix described grandidierite in 1902 from Andrahomana on the southern coast of Madagascar, naming it after French explorer and naturalist Alfred Grandidier, who studied Madagascar's natural history.

True of
grandidierite discovery and name
Numbers
  • 1902 year first described
First fold
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Used inNot in the books yet
2 sources
  1. Mineralogical Society of America Grandidierite (Handbook of Mineralogy) journal
  2. Gemological Institute of America Transparent Grandidierite from Madagascar (Gems & Gemology, Winter 2015) journal, 2015
Discovery and namesEstablished

Musgravite was first described in 1967 from Australia's Musgrave Ranges and takes its name from those desert mountains.

The Handbook of Mineralogy and GIA (2013) report that musgravite (magnesiotaaffeite-6N'3S) was first described in 1967 from the Ernabella Mission area in the Musgrave Ranges of South Australia and named for the locality.

True of
musgravite discovery and name
Numbers
  • 1967 year first described
First fold
Fold 2
Used inNot in the books yet
2 sources
  1. Gemological Institute of America Musgravite from Myanmar (Gems & Gemology, Spring 2013) journal, 2013
  2. Mineralogical Society of America Magnesiotaaffeite-6N'3S / Musgravite (Handbook of Mineralogy) journal
People and careEstablished

Rock collecting is not allowed everywhere: US national parks forbid it, and private land or a mining claim needs the owner's permission.

National Park Service regulations (36 CFR 2.1) prohibit possessing, destroying or disturbing mineral resources in park units, with narrow exceptions. The USGS tells collectors that collecting in national parks and monuments or in state parks is illegal, and to ask permission to collect on private property. BLM rules generally allow reasonable noncommercial collecting on BLM public lands, but not on developed recreation sites, where there are active mining claims, or where the mineral estate is privately owned. BLM's Oregon & Washington rock collecting guide advises against collecting on mining claims without the mining claimant's consent, because the claimant has a legal right to the minerals on the claim. Rules differ by land, so the books say: ask first.

True of
rock and mineral collecting in the United States
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Used inFold 1
4 sources
  1. National Park Service Recreational Collection of Rocks and Minerals—Legal Instruments government
  2. U.S. Geological Survey Collecting Rocks government
  3. Bureau of Land Management Rockhounding government
  4. Bureau of Land Management Rock Collecting Guide: Oregon & Washington government
People and careEstablished

Rock hounds wear safety goggles when they hammer or split rock, because chips can fly.

The USGS tells rock collectors to wear protective clothing, including safety glasses, hard-toed shoes, a hard hat and gloves, when dislodging specimens, and to work with another person if possible. The USDA Forest Service's guide to breaking rock with hand tools says to always wear safety glasses or goggles when picking rock, to guard against flying chips of rock.

True of
rock collecting with hammers and chisels
First fold
Fold 1
Used inFold 1
2 sources
  1. U.S. Geological Survey Collecting Rocks government
  2. USDA Forest Service, Missoula Technology and Development Center Hand Drilling and Breaking Rock for Wilderness Trail Maintenance: Miscellaneous Tips government
People and careEstablished

Shortwave ultraviolet lamps can hurt eyes and skin, so people protect their eyes and skin when they use them.

MiraCosta College's fluorescent-minerals page says shortwave (UVC) light can cause skin burns and eye damage even with short exposure, that eye and skin protection matters when using UV lamps, and shows a shortwave mineral display behind glass; many mineral museums have fluorescent displays. Georgia Tech's UV safety guidance adds that the harm may not show until minutes or hours later, that shields should prevent exposure, and that a handheld UV light is never pointed at a face. The books show the glow in a museum case or as an adult's demonstration.

True of
shortwave (UVC) mineral lamps
Must keep
can
First fold
Fold 1
Used inFold 1
2 sources
  1. MiraCosta College Fluorescent Minerals university, 2022
  2. Georgia Institute of Technology, Environmental Health & Safety Ultraviolet (UV) Safety university
People and careEstablished

Benitoite is California's official state gem.

The California State Capitol Museum lists benitoite as the State Gemstone, designated by the California Legislature in 1985 (Assembly Bill 2357). It was first discovered in 1907 in the San Benito Mountains.

True of
California state symbols
First fold
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Used inNot in the books yet
1 source
  1. California State Capitol Museum Gemstone – Benitoite government
People and careEstablished

The cut kyawthuite gem is kept on display at the Natural History Museum of Los Angeles County so scientists and visitors can study it safely.

Mineralogical Magazine (2017), EarthDate and Wikipedia note that the 1.61-carat faceted kyawthuite holotype specimen is housed at the Natural History Museum of Los Angeles County, preserving the only documented natural sample from destructive testing.

True of
the kyawthuite holotype gem
First fold
Fold 2
Used inNot in the books yet
3 sources
  1. Mineralogical Magazine Kyawthuite, Bi3+Sb5+O4, a new gem mineral from Mogok, Burma (Myanmar) journal, 2017
  2. EarthDate (Switch Energy Alliance) Earth’s Rarest Mineral ngo, 2025
  3. Wikipedia Kyawthuite encyclopedia
Kinds and cousinsEstablished

A rock is made of one or more minerals; a mineral has its own chemistry and crystal structure.

The USGS defines a mineral as a naturally occurring inorganic element or compound with an orderly internal structure and a characteristic chemical composition, crystal form and physical properties (quartz, feldspar, calcite), and a rock as an aggregate of one or more minerals or a body of undifferentiated mineral matter (granite, basalt, limestone). Stone is the series' everyday word for both.

True of
rocks and minerals
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Fold 1
Used inFold 1
1 source
  1. U.S. Geological Survey What is the difference between a rock and a mineral? government
Kinds and cousinsEstablished

Red beryl is a red variety of beryl, the same mineral species as green emerald.

The Utah Geological Survey records that red beryl was identified as a new type of beryl in 1905, with beryl's chemistry Be3Al2Si6O18 and hardness; its red comes from manganese with small amounts of iron, chromium and calcium. GIA describes emerald as the bluish green to green variety of beryl, the mineral species that also includes aquamarine. Red beryl has also been sold as red emerald or bixbite; red beryl is the accepted name.

True of
red beryl
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Used inNot in the books yet
2 sources
  1. Utah Geological Survey Glad You Asked: What gemstone is found in Utah that is rarer than diamond and more valuable than gold? government, 2002
  2. GIA Emerald ngo
Kinds and cousinsEstablished

Tanzanite is the blue to violet variety of the mineral zoisite.

GIA describes tanzanite as the blue-violet variety of zoisite, named by Tiffany & Co. for Tanzania, with colors from violet blue to bluish violet to violet purple; its crystals show different colors in different directions. The USGS Minerals Yearbook (2019) calls it a gemstone variety of zoisite colored by trace vanadium.

True of
tanzanite
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Used inNot in the books yet
2 sources
  1. GIA Tanzanite ngo
  2. U.S. Geological Survey The Mineral Industry of Tanzania in 2019 (2019 Minerals Yearbook) government, 2023
Kinds and cousinsEstablished

Musgravite and taaffeite are close mineral cousins made of beryllium, magnesium and aluminum in slightly different crystal layer stacks.

The Handbook of Mineralogy and GIA (2013) explain that musgravite (magnesiotaaffeite-6N'3S) and taaffeite (magnesiotaaffeite-2N'2S) belong to the same group of beryllium magnesium aluminum oxides, differing in the stacking sequence and ratio of their crystal layers.

True of
musgravite and taaffeite crystal chemistry
First fold
Fold 2
Used inNot in the books yet
2 sources
  1. Gemological Institute of America Musgravite from Myanmar (Gems & Gemology, Spring 2013) journal, 2013
  2. Mineralogical Society of America Magnesiotaaffeite-6N'3S / Musgravite (Handbook of Mineralogy) journal
Lookalikes and testsEstablished

The first known taaffeite was a mauve stone that looked like spinel until Count Taaffe noticed double refraction through it.

Geosciences LibreTexts and National Jeweler report that Count Edward Taaffe was sorting a parcel of cut stones in Dublin in 1945 when he noticed a pale mauve stone that resembled spinel, except that it showed double refraction rather than spinel's single refraction.

True of
the first known taaffeite specimen
Corrects
Taaffeite is a variety of spinel.
First fold
Fold 2
Used inNot in the books yet
2 sources
  1. Geosciences LibreTexts 16.67: Taaffeite university
  2. National Jeweler 5 Things to Know About … Taaffeite news, 2020
Lookalikes and testsEstablished

Because musgravite and taaffeite have nearly identical density and light-bending numbers, gemologists use laboratory laser or X-ray tests to tell them apart.

GIA (Spring 2013) reports that musgravite overlaps taaffeite in refractive indices and specific gravity, so standard desktop gemological tools cannot separate them; Raman spectroscopy or X-ray diffraction is required for a conclusive identification.

True of
separating musgravite from taaffeite
Corrects
Standard magnifying loupes or refractometers can separate musgravite from taaffeite.
First fold
Fold 2
Used inNot in the books yet
2 sources
  1. Gemological Institute of America Musgravite from Myanmar (Gems & Gemology, Spring 2013) journal, 2013
  2. Mineralogical Society of America Magnesiotaaffeite-6N'3S / Musgravite (Handbook of Mineralogy) journal

Myths we avoid

14 popular claims and overstatements the books do not make, and why.

Every gem is a crystal of a mineral.

Some gems are not minerals at all: GIA lists amber as organic, not mineral (fossilized resin), and calls pearls purely organic. Name what each gem is, a mineral, a variety of a mineral or an organic material, rather than calling every gem a mineral crystal.

2 sources
  1. GIA Amber ngo
  2. GIA Pearl ngo

Arthur Pain sieved the first painite out of a river himself.

The sources say Pain first noted the species (Handbook of Mineralogy) or came upon a brownish-red crystal in the Mogok region (EGI); none says how it was taken from the ground or that he sieved it himself. The Handbook places painite in gem gravels near Ohngaing. The premiere's river-sieve scene is an illustration, not a record.

2 sources
  1. Mineralogical Society of America Handbook of Mineralogy: Painite book
  2. Energy & Geoscience Institute, University of Utah ASK EGI: No Painite, No Gain university, 2026

Painite is still the rarest mineral on Earth.

Painite's two-crystal record is historical. Gems & Gemology (2005) reports that the rarity began to change in 2001 and that more than a thousand painite crystals and crystal fragments had been recovered near Mogok by 2005; EGI says that after the early-2000s finds painite was no longer quite the rarest. Say that for many years only two crystals were known, and that gem-quality painite is still rare.

2 sources
  1. Gemological Institute of America Gem News International: New discoveries of painite in Myanmar (Burma), Gems & Gemology, Winter 2005 journal, 2005
  2. Energy & Geoscience Institute, University of Utah ASK EGI: No Painite, No Gain university, 2026

Only one kyawthuite exists in the world.

One crystal is documented: Mineralogical Magazine (2017) bases the mineral's description on a single sample. That is not proof that no second crystal exists, and EarthDate itself says more kyawthuite could possibly exist. Say that scientists know of, or have, one crystal.

2 sources
  1. Mineralogical Magazine Kyawthuite, Bi3+Sb5+O4, a new gem mineral from Mogok, Burma (Myanmar) journal, 2017
  2. EarthDate (Switch Energy Alliance) Earth’s Rarest Mineral ngo, 2025

Red beryl is rarer than diamond (stated as a fact).

The comparison comes from a 2002 Utah Geological Survey article, which says red beryl is so rare that one red beryl crystal is found for every 150,000 diamonds; the article gives no count or method behind that ratio. Attribute it to the survey as a comparison rather than state it as a measured fact.

1 source
  1. Utah Geological Survey Glad You Asked: What gemstone is found in Utah that is rarer than diamond and more valuable than gold? government, 2002

Taaffeite is the only gem ever discovered already cut.

The sources state it as a dated claim of absence: the LibreTexts gemology text says taaffeite is, to date (2007), the only mineral discovered as a faceted gemstone, and National Jeweler (2020) repeats it. Neither is a checked record of every mineral. Keep the modest claim: the first known taaffeite was found already cut.

2 sources
  1. Geosciences LibreTexts 16.67: Taaffeite university
  2. National Jeweler 5 Things to Know About … Taaffeite news, 2020

Every stone is a mineral, and "stone" is a scientific category.

"Stone" is this series' everyday umbrella word, not a scientific category. The USGS defines a mineral as a naturally occurring inorganic element or compound with an orderly internal structure, and a rock as an aggregate of one or more minerals: quartz is a mineral, granite is a rock. A fact names what kind of stone it is about, such as a mineral or a rock.

1 source
  1. U.S. Geological Survey What is the difference between a rock and a mineral? government

Licking or tasting a rock is a safe way to identify it.

Some minerals hold poisons: cinnabar is mercury bonded to sulfur, orpiment and realgar hold arsenic, and galena is lead sulfide. A museum geology curator advises that children not handle galena and that hands be washed after handling such minerals. No book shows or suggests tasting, licking or eating a stone.

2 sources
  1. Denver Museum of Nature & Science Earth's Poisonous Minerals museum
  2. NC Connecting to Collections (guest post by Chris Tacker, Curator of Geology, North Carolina Museum of Natural Sciences) Mineral Hazards museum, 2013

Radioactive minerals are fine to handle, carry in a pocket or keep in a bedroom.

Uranium- and thorium-bearing minerals give off radiation, and some release radon gas. The National Park Service tells museum staff to wear gloves when handling them, wash their hands afterwards, label the cabinets that hold them and, where they release radon, ventilate the room to the outside; Harvard's mineral museum keeps its radioactive minerals off display, in a thick-walled storage room. No book shows a child handling, carrying or keeping one.

2 sources
  1. National Park Service Conserve O Gram 11/10: Radioactive Minerals government, 2006
  2. Harvard Mineralogical & Geological Museum Are radioactive minerals on display? museum

Shortwave UV lamps are safe to shine at stones, skin or eyes.

Short-wave (UVC) light can burn skin and damage eyes even with short exposure, and the harm may not show until minutes or hours later; eye and skin protection matters with UV lamps, and a handheld lamp is never pointed at a face. Fluorescence is shown in a museum display case or as an adult's demonstration, never as something a child tries.

2 sources
  1. Georgia Institute of Technology, Environmental Health & Safety Ultraviolet (UV) Safety university
  2. MiraCosta College Fluorescent Minerals university, 2022

You may dig or take rocks from any park, beach or field.

US national park regulations (36 CFR 2.1) prohibit possessing or disturbing mineral resources in park units, with narrow exceptions. BLM rules generally allow reasonable noncommercial collecting on BLM public lands, but not on developed recreation sites, active mining claims or privately owned mineral estate, and private property needs the owner's permission. The books say: ask first.

3 sources
  1. National Park Service Recreational Collection of Rocks and Minerals—Legal Instruments government
  2. Bureau of Land Management Rockhounding government
  3. U.S. Geological Survey Collecting Rocks government

Crystals or gemstones can heal illness or send out healing energy.

In Christopher French's study at Goldsmiths, University of London (run in 2001 and never published), people meditating with real quartz and with glass fakes reported the same sensations, and they felt what they had been told to expect: the power of suggestion, not of the crystals. French finds no convincing evidence that crystals have healing properties. No book makes a health claim for a stone.

2 sources
  1. TIME You Asked: Do Healing Crystals Actually Work? news
  2. WHYY Why healing crystals might make some people feel better news, 2015

It is safe to hammer or split rocks without eye protection.

The USGS tells rock collectors to wear safety glasses, hard-toed shoes, a hard hat and gloves when dislodging specimens, and to work with another person where possible. Pictures of hammering or splitting rock show eye protection, as Finn wears his safety goggles in the show.

1 source
  1. U.S. Geological Survey Collecting Rocks government

A rare stone is a treasure a child could dig up in the garden, or is sure to be worth a fortune.

Some rare stones are known from only a few places: painite from near Ohngaing village in the Mogok district of Myanmar, and tanzanite from one source, the Merelani Hills of northern Tanzania. GIA names color, clarity, cut and carat weight as what determines a tanzanite's value. Scarcity is not a promise of a likely find or of a fortune.

2 sources
  1. GIA Tanzanite ngo
  2. Mineralogical Society of America Handbook of Mineralogy: Painite book

Back to the six books

From the painite episode of our video series. The Fold 1 book tells this fact too.