Formula: Ca6Si2(CO3)2(SO4)2(OH).24H2O
Origin of name: from Greek thaumasion for to be surprised in allusion to the chemical composition, without parallel at the time of its discovery
Crystal system: Hexagonal
Crystal class: 6
Twinning:
Unit cell: a = 11.03 Å, c = 10.40 Å
Colour: Colourless, white, pale yellow
Diaphaneity: Transparent to translucent
Luster: Vitreous to dull, greasy, silky
Habit: Crystals acicular to filiform, massive, compact, radial
Hardness: 3.5
Specific gravity: 1.88-1.91
Cleavage: 1; {10-11} traces
Tenacity: Brittle, conchoidal fracture
Streak: White
Synonyms/varieties:
Comments: A very late-stage mineral in some sulfide ore deposits. In contact metamorphic zones and from the reaction of geothermal waters or seawaters with basalts and tuffs.
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