Tephroite and knebelite from Hijikuzu Mine, Iwate Prefecture, Japan

Abstract

Tephroite and knebelite samples from the Hijikuzu mine were chemically analyzed by an electron microprobe analysis (EPMA) and examined by X-ray diffraction, optical and DTA methods. The minerals occur as aggregates of small prismatic and/or granular crystals in the bedded manganese ore deposits of the Hijikuzu mine in the highly metamorphosed Jurassic quartzite caused by the Miyako granitic mass. EPMA leads to formulas (Mn1.97Mg0.03Ca0.02)2.02Si0.99O4.00 for tephroite and (Mn1.34Fe2+0.61Mg0.07)2.02Si0.99O4.00 for knebelite.