THE MINERAL CRYOLITE
- Chemistry: Na3AlF6, Sodium Aluminum Fluoride
- Class: Halides
- Uses: as a aid to aluminum processing and other industrial uses and as mineral specimens.
- Specimens
Cryolite is an uncommon mineral of very limited natural distribution. Mostly considered a one locallity mineral, for although there are a few other minor locallities, it was only found in large quantities on the west coast of Greenland.
It was used as a solvent of the aluminum rich ore, bauxite, which is a combination of aluminum oxides such as
gibbsite,
A curious note about cryolite is the fact that it has a low index of refraction close to that of water. This means that if emersed in water, a perfectly clear colorless crystal of cryolite or powdered cryolite will essentially disappear. Even a specimen of cloudy cryolite will become more transparent and its edges will be less distinct, an effect similar to ice in water except that the ice floats.
PHYSICAL CHARACTERISTICS:
- Color is clear or white to yellowish, but can also be black or purple.
- Luster is vitreous.
- Transparency crystals are transparent to translucent.
- Crystal System is monoclinic; 2/m
- Crystal Habits are usually massive and as pseudo-cubic crystals, some with psuedo-octahedral truncations.
- Cleavage is absent, but three parting directions produce what looks like a psuedo-cubic cleavage.
- Fracture is uneven.
- Hardness is 2.5 - 3
- Specific Gravity is 2.95 (average)
- Streak is white.
- Other Characteristics: index of refraction is 1.338 which is close to the index of refraction of water. As a consequence, clear cryolite crystals or powdered cryolite will nearly disappear in water. Also there is no salty taste which is helpful in distinguishing cryolite from the mineral halite.
- Associated Minerals include siderite, quartz, topaz, fluorite, chalcopyrite, galena, cassiterite, molybdenite, columbite and wolframite.
- Notable Occurances include Ivigtut area of Greenland and also at the foot of Pikes Peak at Creede, Colorado, USA, Mont Saint-Hilaire and Francon Quarry, Montreal, Quebec, Canada and at Miask, Russia.
- Best Field Indicators are lack of salty taste, density, index of refraction, locallity and crystal habit.
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