POTASSIC-CARPHOLITE, A NEW MINERAL SPECIES FROM THE SAWTOOTH BATHOLITH, BOISE COUNTY, IDAHO, U.S.A.

Abstract

Potassic-carpholite, ideally (K,) (Li,Mn 2+ )2 Al4 Si4 O12 (OH)4 (F,OH)4, is a new mineral species from the Sawtooth batholith, an anorogenic Tertiary granite pluton near Centerville, Boise County, Idaho, U.S.A. It occurs as irregular tufts (up to 2 mm across) of radiating acicular-to-fibrous crystals in miarolitic cavities in the granite, associated with quartz, microcline, albite, beryl, topaz, bertrandite, hellandite, zinnwaldite, fluorite, hematite and apatite. Individual crystals of potassic-carpholite are white to straw yellow with a white streak and a vitreous luster, and are non-fluorescent in ultraviolet light. Crystals are generally 20‐40 m across and approximately 500 m long and elongate along [100]. Potassic-carpholite is brittle with an irregular fracture on ends of the acicular crystals, and has a perfect cleavage parallel to {010}. Twinning was not observed. The Mohs hardness is ~5, and the observed and calculated densities are 3.08(2) and 3.06 g/cm 3 , respectively. Potassic-carpholite is biaxial negative, with 1.578, 1.592, 1.598, all ±0.002, 2V(obs.) = 57(2)°, 2V(calc.) = 66°, weakly pleochroic with X pale yellow, Y = Z colorless, with X > Y, Z and X = b, Y = a and Z = c. Potassic-carpholite is orthorhombic, space group Ccca, a 13.715(5), b