Crystal forms of borate minerals from the Fuka mine, Okayama Prefecture, Japan

Abstract

Some euhedral crystals of borate minerals were found in vugs and fissures in veins intruded into crystalline limestone near the gehlenite spurrite skarns at the Fuka mine, Okayama Prefecture, Japan. The interfacial angle of the euhedral crystals was measured using a one circle reflecting goniometer. Used euhedral crystals are frolovite, henmilite, hexahydroborite, nifontovite, olshanskyite, pentahydroborite and uralborite. The possible indices of plane and zone axis were calculated from the unit cell parameters of each mineral, and compared with the average values of measurements. The indices of plane and zone axis were determined with maximum error of 1.5 degree between the average value of measurements and calculated value. The crystal forms of frolovite, hexahydroborite, nifontovite, olshanskyite and uralborite are the first report in the world. The crystal forms of henmilite and pentahydroborite reported previously were corrected.