Calciborite from the Fuka mine, Okayama Prefecture, Japan

Abstract

Calciborite was found as a veinlet or a mass in crystalline limestone associated with gehlenite -spurrite skarns at the Fuka mine, Okayama Prefecture, Japan. Calciborite occurs as milky white aggregates up to 1 mm in diameter with shimazakiite, fluorite, bornite and calcite. An electron microprobe analysis of calciborite gave an empirical formula (Ca 0.999 , respectively. The calciborite from the Fuka mine was probably formed by a reaction of boron -bearing fluids with limestone at a temperature between 250 and 300 °C.

Vimsite from the Fuka mine, Okayama Prefecture, Japan

“…The molecular numbers of water within the minerals varies from 0 for calciborite to 6 H 2 O in the molecule of hexahydroborite. According to Kobayashi et al (2014), the density shows a tendency to decrease with increase in the water content in metaborate minerals, and the density calculated for vimsite from the Fuka mine is also in agreement with this tendency. The B 2 O 3 content is almost constant in shimazakiite, sibirskite, priceite, uralborite, and vimsite, and the H 2 O content increases from shimazakiite to vimsite and uralborite, or priceite (Fig.…”

“…The metaborate minerals are characterized by a constant molar ratio CaO:B 2 O 3 = 1:1. Metaborate minerals confirmed from the Fuka mine are vimsite, calciborite (Kobayashi et al, 2014), uralborite (Kusachi et al, 2000), nifontovite (Kusachi and Henmi, 1994), frolovite (Kusachi et al, 1995), pentahydroborite (Fujiwara et al, 1982), and hexahydroborite (Kusachi et al, 1999) (Fig. 4).…”

“…Vimsite occurs with uralborite and priceite in the aggregate of sibirskite, but it is not in direct contact with uralborite in a polymorphic relationship. The other associated minerals are borate minerals such as calciborite (Kobayashi et al, 2014) and kurchatovite (Hayashi et al, 2017) which are spotted in shimazakiite rich parts in the zone, and fluorite, apophyllite, and calcite.…”