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Formula: Hg3S2ClI
Sulphide, mercury-bearing mineral
Crystal System: Monoclinic
Specific gravity: 7.0 measured, 7.05 calculated
Hardness: 2 to 3
Streak: Yellow-orange
Colour: Yellow-orange when fresh, but highly sensitive to sunlight; during exposure it darkens within minutes
through shades of yellow-brown to black
(Mindat).
Environments
Sedimentary environments
Hydrothermal environments
Although radtkeite was approved in 1989, to date (September 2023) it has been reported only from the type
locality.
Localities
At the type locality, the McDermitt Mine, Opalite Mining District, Humboldt County, Nevada, USA, radtkeite
formed during reaction of hydrothermal solutions with lake sediments in the McDermitt caldera complex.
Rhyolitic tuffaceous
sediments accumulated in an ancient lake; those sediments are now strongly altered in places to mixtures of
montmorillonite,
kaolinite, adularia,
opal, cristobalite and
clinoptilolite. Radtkeite was found closely associated with
quartz, cinnabar and
corderoite at one location on the south margin of the present open pit.
Other rare mercury minerals that occur at the McDermitt mine are
calomel, kleinite,
eglestonite, native mercury
and possibly mosesite.
Radtkeite occurs as submicrometer grains, irregular masses, finely dispersed grains in the silica-clay
matrix, coatings on cinnabar and
corderoite, and euhedral crystals up to 10 microns wide and 30 microns
long, most commonly, crystals are tabular prismatic.
The sequence of deposition of sulphides began with early pyrite with
stibnite, followed by cinnabar.
Corderoite was formed when dilute solutions with relatively low
chlorine and sulphur contents reacted with cinnabar. Some
corderoite replaced cinnabar
volume for volume.
The radtkeite may have formed by the reaction of chloride-iodide solutions with
cinnabar, but some was by reaction of iodine with
corderoite as indicated by the common occurrence of radtkeite
with corderoite
(AM 76.1715-1721).
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