Minerals · common

Cryolite

Cryolite is a rare sodium aluminum fluoride mineral, Na3AlF6, historically significant as a flux in the industrial extraction of aluminum metal from bauxite ore. It is best known from a single massive deposit at Ivigtut, Greenland, which was, until its exhaustion, essentially the only commercially significant source on Earth. Its name comes from the Greek for "ice stone," reflecting its unusual property of becoming nearly invisible when submerged in water due to a refractive index close to that of water itself.

Photo: Didier Descouens · Wikimedia Commons · CC BY-SA 3.0

Cryolite properties at a glance

Type	Minerals
Chemical formula	Na3AlF6
Mohs hardness	2.5–3
Crystal system	Monoclinic
Luster	Vitreous to greasy or pearly
Streak	White
Cleavage	None (parting present)
Fracture	Uneven
Specific gravity	2.95–3.0
Transparency	Transparent to translucent
Common colors	Colorless, White, Brownish, Reddish
Rarity	common

Geology & background

Cryolite formed at Ivigtut, Greenland through late-stage hydrothermal or pneumatolytic processes associated with a granite intrusion rich in fluorine, crystallizing within a pegmatite-like body alongside siderite, galena, sphalerite, and other rare fluoride and sulfide minerals. This single deposit was so unusually concentrated that it supplied the world's cryolite for use in the Hall-Héroult process for smelting aluminum until the deposit was mined out in the mid-twentieth century, after which synthetic cryolite manufactured from fluorite became the industrial standard. Small occurrences have since been reported elsewhere, including Colorado's Pikes Peak region, but none approach the historical importance of the Greenland locality.

Collectors should understand that genuine cryolite specimens are quite scarce and command real interest specifically because the Ivigtut deposit is exhausted and no longer accessible for new material. Because natural cryolite is essentially a closed chapter of mineral production, most specimens in collections today trace back to material extracted before mining ceased, making provenance and documentation valuable alongside the specimen itself.

How to identify Cryolite

Cryolite is typically colorless to white, gray, or brownish, with a vitreous to greasy or pearly luster and a white streak. It has a hardness of 2.5 to 3, indistinct cleavage, and a distinctive habit of appearing to nearly disappear when immersed in water because its refractive index is so close to that of water. It can resemble massive quartz or other white fluorides at a glance, but the disappearing-in-water test, combined with its softness and known association with the Ivigtut locality, makes confirmed cryolite readily identifiable.

Compare the specimen's color, luster, crystal habit, grain size, streak, and locality before confirming.
Use multiple photos when possible, including a fresh surface and a close view of texture.

Where Cryolite is found

Reported from multiple localities worldwide; verify locality against specimen provenance when available.

How much is Cryolite worth?

Entry-level specimen	$2
Typical collector specimen	$20
Premium specimen	$150+

Value depends on size, crystal quality, color, locality, rarity, damage, and provenance.

Common uses

Collector specimens
Education
Field identification
Industrial or lapidary use when suitable

Interesting facts

Cryolite becomes almost invisible when dropped into a glass of water because its refractive index nearly matches that of water itself.
For decades, virtually the entire world's supply of natural cryolite came from a single deposit at Ivigtut, Greenland, now completely mined out.
Before synthetic alternatives were developed, cryolite served as the essential flux that lowered the melting point of alumina in the industrial process used to smelt aluminum metal.