bityite

{{Infobox mineral | name = Bityite | category = Phyllosilicate minerals | group = Mica group, brittle mica group | image = | alt = | caption = | formula = CaLiAl2(AlBeSi2)O10(OH)2 |IMAsymbol=Bty | molweight = | strunz = 9.EC.35 | dana = 71.02.02c.03 | system = Monoclinic | class = Prismatic (2/m) (same H-M symbol) | symmetry = C2/c | color = Pearly white, grayish blue, greenish blue, light brown | colour = | habit = Dense, micaceous aggregates or rosettes and encrustations | twinning = | cleavage = Perfect micaceous on {001} | fracture = Uneven | tenacity = | mohs = 3 | luster = Vitreous, pearly on cleavages | streak = | diaphaneity = Transparent to translucent | gravity = 5.5 | density = | polish = | opticalprop = Biaxial (-) | refractive = nα = 1.651 nβ = 1.659 nγ = 1.661 | birefringence = δ = 0.010 | pleochroism = | 2V = Measured: 35° to 52° | dispersion = Strong | extinction = | length fast/slow = | fluorescence= | absorption = | melt = | fusibility = | diagnostic = | solubility = | other = | alteration = | references = }} Bityite is considered a rare mineral, and it is an endmember to the margarite mica sub-group found within the phyllosilicate group. The mineral was first described by Antoine François Alfred Lacroix in 1908, and later its chemical composition was concluded by Professor Hugo Strunz. Bityite has a close association with beryl, and it generally crystallizes in pseudomorphs after it, or in cavities associated with reformed beryl crystals. The mineral is considered a late-stage constituent in lithium bearing pegmatites, and has only been encountered in a few localities throughout the world. The mineral was named by Lacroix after Mt. Bity, Madagascar from where it was first discovered.

==Geologic occurrence==