Formula: (Ca,Na)Al2Si6O16.4-8H2O
Origin of name: for R. Tschernich, American mineralogist
Crystal system: tetragonal
Crystal class: 4/m 2/m 2/m
Twinning: common on {302}, {101} or {304} contact or repeated
Unit cell: a = 12.88 Å, c = 25.02 Å
Colour: colourless to white
Diaphaneity:
Luster: vitreous
Habit: 0.1 to 10 mm steep tetragonal dipyramids in cavities in basalt, drusy linings, radiating hemispherical groups
Hardness: 4.5
Specific gravity: 2.02
Cleavage: none
Tenacity: conchoidal, brittle
Streak: white
Synonyms/varieties:
Comments: sometimes fluoresces pale yellow under LW and SW ultraviolet light
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