Afghanite

Formula:  (Na, Ca, K)₈(Si, Al)₁₂O₂₄(SO₄, Cl, CO₃)₃.H₂O

Origin of name:  after country of discovery, Afghanistan

Crystal system:  Hexagonal

Crystal class:  6mm or 6/m 2/m 2/m or -6 m2

Twinning:

Unit cell: a = 12.77 Å, c = 21.35 Å

Colour:  Bluish, colourless

Diaphaneity: Transparent

Luster:  Vitreous

Habit:  Crystals thin tabular; massive

Hardness:  5.5 to 6

Specific gravity: 2.55

Cleavage:  1: perfect on {10-10}

Tenacity:

Streak: White

Synonyms/varieties:

Comments: Member of the cancrinite group. Found in thin veinlets cutting lazurite crystals, in silicified limestone xenoliths in pumice