Grechishchevite

grechishchevite

kuzminite

kadyrelite

lavrentievite

Images

Formula: Hg3S2BrCl0.5I0.5
Sulphide of mercury, containing bromine, chlorine and iodine
Crystal System: Tetragonal
Specific gravity: 7.23 measured on synthetic material, 7.16 calculated
Hardness: 2½
Streak: Deep yellow to yellow with a slight orange tint
Colour: Bright or dark orange, slowly darkening to brown-orange, then black
Solubility: Fragments blacken in 40% KOH; unaffected by HCl or HNO3
Environments

Hydrothermal environments

Although grechishchevite was approved in 1988, to date (February 2025) it has been reported only from the type localities.

Localities

There are two co-type Localities, the Arzak Hg occurrence, and the Kadyrel' Hg occurrence, Oorash-Khem River Valley, both in the Uyuk Range, Pi-Khem District, Tuva, Russia. At the type localities grechishchevite occurs on fracture walls as films consisting of minute prisms and groups of equant to slightly elongate grains to 0.2 mm (Arzak occurrence), and also as powdery masses and as concretions of short prismatic crystals to 0.3 mm (Kadyrel occurrence). It occurs sporadically in oxidized cinnabar ores at the Arzak deposit and less frequently in leached voids at Kadyrel, in association with numerous other mercury minerals that include calomel, kuzminite, cordierite, kadyrelite, lavrentievite and eglestonite (AM 76.1728-1735).
Grechishchevite from the Kadyrel' Hg occurrence - Image

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