Formula: (Ca,Mn)4Be3Si6O17(OH)4.3H2O
Origin of name: after locality Tvedalen area, Norway
Crystal system: orthorhombic
Crystal class: 2/m
Twinning:
Unit cell:
Colour: white, pale gray, beige
Diaphaneity:
Luster: vitreous
Habit: platelets to a few micron forming spherules to 3 mm
Hardness: 4.5
Specific gravity: 2.54
Cleavage: 1; {010} perfect
Tenacity:
Streak: white
Synonyms/varieties:
Comments:
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