Images
Formula: Tl2AgCu2As3S7
Sulphosalt, sulpharsenite,
thallium-bearing mineral
Crystal System: Triclinic
Specific gravity: 5.38 calculated
Hardness: 1½ to 2
Streak: Blackish red
Colour: Grey to black
Environments
Metamorphic environments
Hydrothermal environments
Although gabrielite was approved in 2002, to date (January 2026) it has been reported only from the type locality.
Localities
At the type locality, the Lengenbach Quarry, Fäld, Binn, Goms, Valais, Switzerland, gabrielite, with a
thallium content of 37.4 wt%, is among the minerals richest in
thallium occurring at Lengenbach; only
imhofite, with 37.6 wt%, contains slightly more
thallium. As in the case of the other
minerals of thallium, gabrielite is only found in the zone with elevated
thallium and arsenic contents, and
consequently it is commonly accompanied by realgar,
rathite, trechmannite,
tennantite, hutchinsonite,
hatchite, edenharterite and other
thallium-rich sulphosalts. All these minerals crystallised in small irregularly
shaped cavities in the dolomitic rock. The
thallium-rich minerals, in particular, are the products of the latest stage of
hydrothermal activity at Lengenbach. It was the very peculiar shape of some of the very small crystals (individual crystals
not exceeding 0.4 mm), that piqued scientific interest in the mineral; the crystals show a conspicuous sixfold outline,
though from the distinct striation on the largest face, hexagonal symmetry can be ruled out. In its anhedral form,
gabrielite is almost indistinguishable from other Lengenbach thallium
minerals, in particular sicherite, therefore, any material used for analytical
work had to be verified first by X-ray diffraction. However, the pseudohexagonal shape (where present), the perfect
cleavage, the black metallic appearance and the reddish streak (clearly visible on broken edges) might give some indication
of its identity. With a Mohs hardness of 1½ to 2, gabrielite has the lowest hardness among all Lengenbach
thallium sulfosalts
(CM 44.1.135-140).
Gabrielite from the Lengenbach Quarry -
Image
Back to Minerals