Cancrinite

Formula:  Na₆Ca₂Al₆Si₆O₂₄(CO₃)₂

Origin of name:  For Count Cancrin (1774-1845), German-Russian Minister of Finance of Russia

Crystal system: Hexagonal

Crystal class: 6

Twinning: lamellar, rare

Unit cell: a = 12.58-12.76 Å, c = 5.11-5.20 Å

Colour: Colourless, white, light blue to light grayish blue, honey-yellow, orange, reddish, pinkish

Diaphaneity: Transparent to translucent

Luster: Vitreous, pearly, or greasy

Habit: Rarely as prismatic crystals, terminated by a low pyramid, to 2 cm, commonly massive

Hardness: 5-6

Specific gravity: 2.42-2.51

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

Tenacity: Brittle, uneven fracture

Streak: White

Synonyms/varieties: 

Comments:  Series with vishnevite. Primary mineral in some alkalic igneous rocks, including pegmatites in nepheline syenites, also as alteration of nepheline