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Nifontovite and olshanskyite from Fuka, Okayama Prefecture, Japan

Published online by Cambridge University Press:  05 July 2018

Isao Kusachi  and
Chiyoko Henmi
Isao Kusachi
Affiliation:
Department of Earth Sciences, Faculty of Education, Okayama University, Okayama 700, Japan
Chiyoko Henmi
Affiliation:
Department of Earth Sciences, Faculty of Science, Okayama University, Okayama 700, Japan
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Abstract

Nifontovite and olshanskyite, two rare hydrous calcium borate minerals, have been found in crystalline limestone near gehlenite-spurrite skarns at Fuka, Okayama Prefecture. Nifontovite occurs as aggregates of tabular crystals up to 5 cm long and 1.5 cm wide, and rarely as euhedral crystals up to 1 mm long. Olshanskyite occurs as anhedral masses, or as micro-twinned platy crystals up to 1 cm long. Wet chemical analyses give the empirical formulae Ca3.052B5.991O6.038(OH)12·1.96H2O and Ca2.888B3.997(OH)18 on the basis of O = 20 for nifontovite and OH=18 for olshanskyite, respectively. The formulae are consistent with those from type localities.

The X-ray powder data for these minerals were determined with accuracy. The unit cell parameters of nifontovite agree closely with those published previously. X-ray studies show that olshanskyite is triclinic with the possible space group P1̄ or P1 and a = 9.991(5), b = 14.740(11), c = 7.975(3) Å, α = 94.53(4), β = 69.08(3), γ = 112.44(5)° and Z = 3. The density 2.19 g cm−3 (meas.) obtained for olshanskyite agrees with the estimated ideal value 2.31 g cm−3 (calc.). Nifontovite was formed by hydrothermal alteration of an anhydrous borate, and olshanskyite was formed by hydrothermal alteration of nifontovite and the anhydrous borate.

Keywords

nifontoviteolshanskyiteborateskarncrystalline-limestoneFukaJapan
Type
Mineralogy
Information
Mineralogical Magazine , Volume 58 , Issue 391 , June 1994 , pp. 279 - 284
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1994

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