Aphthitalite

Formula:  (K,Na)₃Na(SO₄)₂

Origin of name:  From Greek for unchangeable and salt

Crystal system:  Hexagonal

Crystal class:  -3 2/m

Twinning:

Unit cell:

Colour:  Colourless, white, grey, greenish, blue, or reddish due to inclusions

Diaphaneity: Transparent to opaque

Luster:  Vitreous to resinous

Habit:  Crystals thin to thick tabular; pseudo-hexagonal twins resembling Aragonite; massive; crust; bladed aggregates

Hardness:  3

Specific gravity:  2.66 to 2.71

Cleavage:  2; {10-10} fair, {0001} poor

Tenacity:

Streak: White

Synonyms/varieties: Glaserite

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