Yarzhemskiite

yarzhemskiite

strontioginorite

satimolite

carnallite

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Formula: K[B5O7(OH)2].H2O
Pentaborate
Crystal System: Monoclinic
Specific gravity: 2.13 measured, 2.112 calculated for the empirical formula
Hardness: 2½
Streak: White
Colour: Colourless
Luminescence: Non-fluorescent under both UV and an electron beam
Environments

Salt domes

Yarzhemskiite is a relatively new mineral, approved in 2018 and to date (March 2025) reported only from the type locality.

Localities

At the type locality, Borehole no. 800, Chelkar salt dome, Aksai Valley, Shalkar District, Aktobe Region, Kazakhstan, yarzhemskiite was found in core of the borehole as separate crystals or grains having irregular outlines embedded in a halitesylvite rock. Other associated minerals are carnallite, polyhalite, gypsum, strontioginorite, satimolite and quartz.
Yarzhemskiite was formed as a result of diagenesis or of the post-diagenesis processes in boron-bearing evaporite rocks. It is likely that the formation of yarzhemskiite and associated borates accompanies the recrystallisation of the halitesylvite rock. Crystals of yarzhemskiite are thick tabular, slightly elongate (short prismatic) or equant, commonly coarse, with a sculptured and/or cavernous surface. Well-formed crystals are up to 0.5 mm × 0.7 mm × 1 mm (typically much less) whereas grains having irregular outlines are up to 1 mm × 1.5 mm × 2 mm. The crystals typically contain inclusions of halite, sylvite and quartz. Yarzhemskiite is transparent and colourless, with a white streak and vitreous lustre (MM 84.335–342).

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