Optical Properties: Translucent. Color: Pale yellow, straw-yellow, yellowish green, greenish gray, nearly white; colorless to pale yellow in transmitted light. Luster: Pearly, silky in

aggregates. Optical Class: Biaxial (+), anomalous. Pleochroism: Colorless to pale amber-yellow. Orientation: Z = c. = 1.518‐1.533 (variable with H 2 O content) = 1.518‐1.535 = 1.561‐1.575 2V(meas.) = 0 Cell Data: Space Group: R3. a = 24.176 c = 7.656 Z = 18