Formula: Na2(Ti,Fe)Si4(O,F)11
Origin of name: after locality Narsarsuk, Greenland
Crystal system: tetragonal
Crystal class: 4/m
Twinning:
Unit cell: a = 10.72 Å, c = 7.955 Å
Colour: colourless, white, yellow, green, brown
Diaphaneity:
Luster: vitreous
Habit: crystals short prismatic or tabular
Hardness: 6 to 7
Specific gravity: 2.78
Cleavage: 2; {100} and {110} perfect
Tenacity: uneven, brittle
Streak:
Synonyms/varieties: gouréite
Comments:
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