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Formula: Pb2As2S5
Sulpharsenite,
sartorite group, forms a series with
veenite
Crystal System: Monoclinic
Specific gravity: 5.50 to 5.57 measured, 5.61 calculated
Hardness: 3
Streak: Reddish brown, chocolate brown
Colour: Dark lead-grey, dark red-brown in transmitted light
Environments
Metamorphic environments
Hydrothermal environments
Dufrénoysite is an uncommon mineral of medium to low temperature hydrothermal origin. Associated minerals include
chalcopyrite, sphalerite,
realgar, orpiment and
tetrahedrite
(HOM).
Localities
The type locality is the Lengenbach Quarry, Fäld, Binn, Goms, Valais, Switzerland. It has been suggested that the
Lengenbach deposit was originally a sulphide-dolomite deposit containing
galena and sphalerite, which was
invaded by arsenic-rich hydothermal fluids that introduced
copper, silver and
tellurium in addition to arsenic
into the deposit. The lead-arsenic sulphide minerals were formed during
metamorphism and hydrothermal alteration with the least arsenic-rich minerals
forming first and being progressively replaced by the more arsenic-rich
minerals as the reactions progressed. According to this hypothesis, the first
lead-arsenic mineral to form at Lengenbach
was jordanite, which is not simply structurally related to the
sartorite group minerals. Jordanite
was followed, in sequence, by dufrénoysite, liveingite,
baumhauerite, rathite
and sartorite.
It was concluded that two separate paragenetic sequences leading to the formation of the
sartorite-group minerals are required to account for the formation of
liveingite and rathite.
The flrst sequence is dufrénoysite to liveingite to
baumhauerite to sartorite.
The second sequence is dufrénoysite to rathite to
sartorite.
The first sequence appears to be dominant at Lengenbach since liveingite,
baumhauerite and sartorite are
relatively common in the deposit, whereas rathite is very rare.
Liveingite has not been found with
sartorite, nor baumhauerite
with dufrénoysite
(AM 75.289-294).
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