Carpholite

(repeating unit)Mn²⁺Al₂Si₂O₆(OH)₄IMA symbolCar^[1]Strunz classification9.DB.05Crystal systemOrthorhombicCrystal classDipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)Space groupCccaUnit cella = 13.83, b = 20.31,
c = 5.13 [Å]; Z = 8IdentificationColorYellowCrystal habitPrismatic, acicular to fibrous clustersTwinningOn {100}CleavagePerfect on {010}TenacityBrittleMohs scale hardness5.5-6LusterSilkyDiaphaneityTranslucentSpecific gravity2.935-3.031Optical propertiesBiaxial (-)Refractive indexn_α = 1.610 n_β = 1.628
n_γ = 1.630Birefringenceδ = 0.020PleochroismDistinct; X = Y = pale yellow;
Z = colorlessReferences^[2][3][4]

Carpholite is a manganese silicate mineral with formula Mn²⁺Al₂Si₂O₆(OH)₄. It occurs as yellow clusters of slender prisms or needles. It crystallizes in the orthorhombic system.

The carpholite group includes ferrocarpholite, magnesiocarpholite, vanadiocarpholite, and potassiccarpholite.

Discovery and occurrence

It was first described in 1817 for an occurrence in Horní Slavkov (Schlaggenwald), Karlovy Vary Region, Bohemia. The name derives from Greek karfos for "straw" and lithos for "stone" due to its crystal habit.^[4]

Its typical occurrence is in shales that have undergone low grade metamorphism. Associated minerals include sudoite, manganoan garnet, chloritoid and fluorite.^[2]

References