page_title: Cryolite
section_title: Physical properties
hierarchical_section_title: Cryolite / Physical properties
caption_attribution_description: Cryolite unit cell 3D polyhedra
context_page_description: Cryolite is an uncommon mineral identified with the once-large deposit at Ivittuut on the west coast of Greenland, depleted by 1987.
  Due to its rarity it is possibly the only mineral on Earth ever to be mined to commercial extinction.
context_section_description: Cryolite occurs as glassy, colorless, white-reddish to gray-black prismatic monoclinic crystals. It has a Mohs hardness of 2.5 to 3 and a specific gravity of about 2.95 to 3.0. It is translucent to transparent with a very low refractive index of about 1.34, which is very close to that of water; thus if immersed in water, cryolite becomes essentially invisible.
caption: Cryolite's unit cell.  Sodium atoms are purple; fluorine atoms are pale green, arranged in octahedra around an aluminium atom.
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