Wollastonite
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Wollastonite is a calcium inosilicate mineral that may contain small amounts of iron, magnesium, and manganese substituting for calcium. It is usually white. Wikipedia
Chemical formula: CaSiO3
2V angle: Measured: 36° to 60°
Cleavage: Perfect in two directions at near 90°
Color: White, colorless or gray
Crystal class: Pinacoidal (1); (same H-M symbol)
Crystal habit: Rare as tabular crystals—commonly massive in lamellar, radiating, compact and fibrous aggregates
Crystal system: Triclinic; Monoclinic polytype exists