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Formula: CuMg(SO4)2
Sulphate
Crystal System: Monoclinic
Specific gravity: 3.508 calculated for the empirical formula
Hardness: 3½
Streak: White
Colour: Light-blue to colourless, light brown
Luminescence: Non-fluorescent under ultraviolet rays or an electron beam
Solubility: Water soluble and hydroscopic
Environments
Dravertite is a relatively new mineral, approved in 2015 and to date (July 2024) reported only from the
Tolbachik Volcanic field, where it forms sublimates around active fumaroles
(HOM).
Localities
At the type locality, the Arsenatnaya fumarole, Second scoria cone, Northern Breakthrough, Great Fissure eruption,
Tolbachik Volcanic field, Milkovsky District, Kamchatka Krai, Russia, the holotype of dravertite was
collected from the fumarole located near the summit of the Second scoria cone. In some areas dravertite is a
common constituent, closely associated with dolerophanite,
euchlorine, tenorite,
hematite, langbeinite,
steklite, fedotovite,
wulffite, anhydrite,
anglesite and an incompletely characterised sodium-copper-magnesium
sulphate. The temperature measured in these areas (inside cracks and chambers) immediately after their uncovering was
360 to 370°C. Only H-free minerals occur in this hot zone. Upwards, near day surface, in the areas with temperatures
lower than 150°C, the “dry” sulphate mineralisation alters under the influence of atmospheric humidity with formation
of the supergene assemblage including hydrous sulphates,
typically chalcanthite,
bonattite, kaliochalcite,
epsomite, hexahydrite and
gypsum.
In the Arsenatnaya fumarole, dravertite occurs as crusts up
to 5 x 5 cm2 in area and usually up to 3 mm, rarely up to 1 cm, thick, overgrowing
basalt scoria altered by
fumarolic gas. The crusts contain numerous micro-cracks and caverns. Dravertite forms intimate intergrowths
with dolerophanite and/or
euchlorine, and its aggregates are commonly impregnated by
micro-inclusions of a sodium- and copper- bearing variety of langbeinite
and an incompletely characterised sodium-copper-magnesium sulphate. Rarely, dravertite occurs as compact
clusters of crude equant crystals up to 0.08 mm in size
(EJM 29.2.323-330).
Dravertite from the Arsenatnaya fumarole -
Image
At the Yadovitaya fumarole, Second scoria cone, Northern Breakthrough, Great Fissure eruption, Tolbachik Volcanic
field, Milkovsky District, Kamchatka Krai, Russia, in July 2015, dravertite was found in the fumarole where
the temperature was measured as 290 to 300°C. Dravertite forms here as crusts up to 1 x 2 cm2 in
area and up to 1 mm thick. Associated minerals are euchlorine,
chalcocyanite, steklite,
alumoklyuchevskite,
piypite, parawulffite,
cryptochalcite,
dolerophanite, hematite,
tenorite, vergasovaite,
cupromolybdite,
yaroshevskite and ziesite.
Dravertite is one of the latest sublimate sulphates here. Its crusts overgrow encrustations of
euchlorine sometimes covering
chalcocyanite crystals. Hence the sequence of deposition of major
copper sulphates forming this assemblage is first chalcocyanite then
euchlorine and lastly dravertite
(EJM 29.2.323-330).
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