Formula: Ca2(Mg,Fe)5Si8O22(OH)2
Origin of name: after locality Tremola Valley, St. Gotthard, Switzerland
Crystal system: monoclinic
Crystal class: 2/m
Twinning: common on {100} simple or lamellar, rare on {001} lamellar
Unit cell: a = 9.84 Å, b = 18.02 Å, c = 5.27 Å, b = 105.0°
Colour: colourless, white, gray, pale greenish, pink
Diaphaneity:
Luster: vitreous
Habit:
Hardness: 5 to 6
Specific gravity: 2.9 to 3.2
Cleavage: 2; {110} good, {100} parting
Tenacity:
Streak:
Synonyms/varieties: abkhazite, byssolite (fibrous variety), calamite, grammatite, hexagonite (Mn-rich variety), hoepfnerite, nephrite (compact variety), nordenskiöldite
Comments: member of amphibole group, series with actinolite and ferro-actinolite
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