Cryolite

A curiosity mineral. Colourless samples of this sodium-aluminium-fluoride mineral seemingly disappear in water due to the proximity of their refractive indices. Historically, cryolite was used as an aluminium ore (Ivigtut, Greenland) and later in the electrolytic processing of the aluminium ore bauxite.

History

Activities related to discovery and approval of the group members

Structural context

Cryolite
Crystal System monoclinicSpace Group P21/c
a5.392—7.935 (5.6926)
b5.55—7.935 (5.8143)
c7.739—7.9619 (7.8455)
alpha90
beta89.81—90.278 (90.0923)
gamma90
volume231.593—499.621 (263.5247)

Based on 23 measurements

Chemical context

Stoichiometric formulas

Cryolite
mindat.org
  • March 13, 2023Na2NaAlF6
IMA
  • March 13, 2023Na2NaAlF6
mineralogy.rocks
  • Aug. 30, 2022Na3AlF6

Elements recorded on EPMA

20
Al
20
F
20
Na

Physical properties

ColorColor entities, recognized using a custom trained NER model
  • colourless
  • colourless
          Color noteOriginal color note from the source
          Colourless, white, brown, grey, black; colourless in transmitted light.
          StreakStreak entities, recognized using a custom trained NER model
            Streak noteOriginal streak note from the source
            White
            Lustre
            Vitreous
            Greasy
            Pearly
            Fracture
            Irregular/Uneven
            Transparency
            Transparent
            Translucent
            Tenacity
            brittle
            Hardness
            3—3.5
            Measured density
            2.96—2.98
            Calculated density
            2.973