Chiyokoite

Images

Formula: Ca₃Si(CO₃)[B(OH)₄]O(OH)₅.12H₂O
Carbonate, monoborate, ettringite group,
Crystal System: Hexagonal
Specific gravity: 1.85 measured, 1.85 calculated
Streak: White
Colour: Pink to colourless
Luminescence: Not fluorescent under UV
Environments

Metamorphic environments
Hydrothermal environments

Chiyokoite is a relatively new mineral, approved in 2019 and to date (February 2024) reported only from the type locality

Localities

At the type locality, the Fuka mine, Fuka, Bitchū, Takahashi City, Okayama Prefecture, Japan, chiyokoite is a low-temperature hydrothermal mineral formed in cavities of a hydrothermally altered, boron-bearing, low-Fe calc-silicate skarn, together with calcite, henmilite and tacharanite. Chiyokoite occurs as hexagonal prismatic crystals up to 30 microns long and up to 20 microns thick. The crystals are combined in clusters which form, together with intimately associated calcite, friable nests up to 1 cm across and up to 1 mm thick in tacharanite-calcite incrustations.
Chiyokoite is pink to colourless with a white streak and vitreous lustre (CM 58.5.653-662).
Image

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