Lawsonite
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Lawsonite is a hydrous calcium aluminium sorosilicate mineral with formula CaAl₂Si₂O₇(OH)₂·H₂O. Lawsonite crystallizes in the orthorhombic system in prismatic, often tabular crystals. Crystal twinning is common. Wikipedia
Optical properties: Biaxial (+)
Cleavage: Perfect on, and, imperfect on
Pleochroism: Weak; X = blue, pale brownish yellow; Y = deep bluish green, yellowish green; Z = colorless, yellowish
Density: 3.09
2V angle: Measured: 84°–85°
Birefringence: δ = 0.019–0.021
Color: Colorless, white, pale blue to grayish blue