Anthophyllite
Anthophyllite is an orthorhombic amphibole mineral: ☐Mg₂Mg₅Si₈O₂₂(OH)₂, magnesium iron inosilicate hydroxide. Anthophyllite is polymorphic with cummingtonite. Some forms of anthophyllite are lamellar or fibrous and are classed as asbestos. Wikipedia
Birefringence: δ = 0.017 – 0.023
Cleavage: Perfect on, imperfect on
Color: Gray to green, brown, and beige
Crystal class: Dipyramidal (mmm); H-M symbol: (2/m 2/m 2/m)
Crystal habit: Rarely as distinct crystals. Commonly lamellar or fibrous
Crystal system: Orthorhombic
Formula (repeating unit): ☐Mg2Mg5Si8O22(OH)2