Coccinite from the burning dump of Almaznaya coal mine (Eastern Donbass) – the first find in Russia

An extremely rare mercury iodide coccinite, HgI2, was found in a burning dump of the Almaznaya coal mine (near the settlement of Gukovo, Rostov oblast, Russia). It forms bright red tabular and short-prismatic crystals with adamantine luster up to 0.5 mm in size on a crust of native sulfur, which flls the fractures in the burnt rock. This is the frst fnd of coccinite in the Russian Federation. The refectance values and quantitative chemical analysis of coccinite are published for the frst time. The chemical composition of the mineral is as follows (wt. %, mean of fve analyses, electron microprobe): Hg 45.15, Cl 0.11, Br 0.65, I 53.91, total 99.82. The empirical formula calculated based on sum of three atoms is Hg1.02I1.93Br0.04Cl0.01. The strongest refections of the powder X-ray diffraction diagram are [d,A(I)(hkl)]: 6.220(29)(002), 4.122(82) (101), 3.575(100)(102), 3.008(37)(103), 2.767(35)(112), 2.189(98)(114, 200). The parameters of the tetragonal unit cell calculated from the powder data are as follows: a = 4.3744(2), c = 12.4301(7) A, V = 237.86(2) A3. Coccinite crystallized from hot gases after the combustion of coal-bearing rocks in the inner part of the dump.