Crystal structure of the epidote from Osayama, Okayama Prefecture, Japan

Abstract

The crystal structure and the crystallochemical properties of a epidote from Oosa-yama area, Okayama Prefecture, Japan wa investigated by the XRD, EPMA, single-crystal X-ray diffraction and Moessbauer spectroscopy. The chemical composition of the specimen was determined as Ca_2.164(Al_2.411Fe³⁺_0.451)_2.862Si_3.014O_12.000(OH)_1.026. The cell parameters were a=8.886, b=5.606, c=10.150 A, beta=115.4 deg, monoclinic, P2₁/c. The final R-factor for thestrucutre determination was 0.031. The X_ps = Fe³⁺/(Fe³⁺+Al) was determined as 0.1576.The hydrogen bonding in the structure was formed as O(4)-H-O(10). The angle of the hydrogen bonding was determined as 117.6 deg. Compare with previous structural works, the hydrogen bonding angles were proportional to the X_ps. The Fe³⁺ contents accomodated in the M1 and M3 sites were determined by the Moessbauer spectroscopy, X_Fe³⁺,M1=0.061and X_Fe³⁺,M3=0.099, respectively. But the nonequilibrium ordering state for the specimen was not clearly determined in this work.