Clinohumite
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Clinohumite is an uncommon member of the humite group, a magnesium silicate according to the chemical formula (Mg, Fe)₉(SiO₄)₄(F, OH)₂. The formula can be thought of as four olivine, plus one brucite. Indeed, the mineral is essentially a hydrated... Wikipedia
Color: Brownish to orange, yellow, red
Crystal class: Prismatic (2/m); (same H-M symbol)
Crystal habit: Granular, prismatic, twinned
Crystal system: Monoclinic
Formula (repeating unit): (Mg,Fe)9(SiO4)4(F,OH)2
Luster: Vitreous to resinous
Optical properties: biaxial (+)