Cryolite is a rare sodium aluminum fluoride most famous for its primary historic occurrence in Ivigtut, Greenland, where it formed a massive deposit. It is notable for having a refractive index very close to that of water, making it appear to disappear when immersed in a glass of water. It typically occurs as massive, white to colorless granular masses rather than well-defined crystals.
Is this cryolite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch cryolite with a known reference. Cryolite sits at Mohs 2.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous to greasy or waxy, pearly on {001}.
- 4Match the color rangeCompare against the expected color range: white, colorless, yellowish, reddish, brownish, brownish black, gray, reddish brown.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: euhedral crystals, massive.
Often confused with
Cryolite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Quartz is the harder of the two (Mohs 7 vs. 2.5).
How to tell apart: Fluorite is the harder of the two (Mohs 4 vs. 2.5).
How to tell apart: Albite is the harder of the two (Mohs 6-6.5 vs. 2.5).
Often found alongside cryolite
Minerals reported to co-occur with cryolite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Na₃AlF₆
- Mohs hardness
- 2.5
- Density
- 2.97 g/cm³
- Streak
- White
- Luster
- Vitreous to greasy or waxy, pearly on {001}
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
- Crystal habit
- Euhedral crystals, massive
- Cleavage
- Partings on {001} and {110}
- Fluorescence
- Bluish white under SW UV
- Rarity
- Rare
- Uses
- Collector, Industrial (formerly for aluminum smelting)
- Host rock
- A late-stage mineral in some granite pegmatites; in tin-bearing alkalic granites; a vapor-phase mineral along fractures and in the groundmass of some fluorine-rich, topaz-bearing rhyolites
Where rockhounds find cryolite
Classic worldwide localities
- St. Peters Dome, near Pikes Peak, El Paso Co., in the Goldie carbonatite, Fremont Co., and the Green River Formation, Colorado, USA
- Round Top intrusion, Sierra Blanca Peaks, Hudspeth Co., Texas, USA
- Zapot pegmatite, 25 km northeast of Hawthorne, Fitting district, Mineral Co., Nevada, USA
- Morefield pegmatite, Amelia, Amelia Co., Virginia, USA
- Ivigtut, southwestern Greenland
- Francon quarry, Montreal Island, Montreal, at Mont Saint-Hilaire, and from near Saint-Amable, Quebec, Canada
Field-hunting tip
Where it forms: A late-stage mineral in some granite pegmatites; in tin-bearing alkalic granites; a vapor-phase mineral along fractures and in the groundmass of some fluorine-rich, topaz-bearing rhyolites. If you start seeing pachnolite, thomsenolite, gearksutite in float, you are in the right ground. Typical habit: euhedral crystals, massive. Train your eye for that shape before scanning the outcrop.
Common questions
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Find cryolite on the map
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