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Formula: (Ni,Co)30(As2O7)15
Arsenate, nickel- and
cobalt- bearing mineral
Crystal System: Monoclinic
Specific gravity: 4.904 calculated for the empirical formula
Hardness: Less than 5
Streak: pale reddishbrown to pale purplish brown
Colour: Dark violet-red to dark brownish red
Luminescence: Not fluorescent under long wave or short-wave UV
Common impurities: Ca,Cu,Fe
Environments
Localities
At the type locality, Johanngeorgenstadt, Erzgebirgskreis, Saxony, Germany, a single specimen containing
petewilliamsite was found in an old mineral shop in Germany in 1981. The bulk of the specimen, which measures
7 x 5 x 4 cm3 and was probably mined in the mid-1800s, consists of a fine-grained
quartz matrix with several veins of
nickeline, up to 4 mm thick, dispersed throughout. The
nickeline veins are rimmed by
native bismuth which, in turn, is rimmed by an intergrowth of very darkgreen
crystals of bunsenite, up to 1 mm in size. Colourful
secondary minerals richly cover significant areas of the sample.
These include grass-green aerugite crystals and crystal aggregates, with
euhedral crystals up to 1 mm in size, varicoloured yellow to light yellowbrown to brownish purple
xanthiosite with rare euhedral crystals up to 0.5 mm in size, colourless to
white adamantine crystals of rooseveltite up to 1 mm in size in several
vugs, crystals and crystalline masses of orange-brown to deep golden brown
paganoite intimately associated with
aerugite, deep blue crusts of an undefined
nickel - cobalt -
arsenate phase, intimately associated with
quartz, and an undefined nickel -
cobalt - copper - potassium -
bismuth - arsenate phase, which occurs
as micron-sized inclusions within petewilliamsite. The petewilliamsite is a
secondary phase most likely formed from the breakdown of
primary nickeline.
Petewilliamsite mainly occurs in scattered patches of mm-sized aggregates, intimately associated with
varicoloured xanthiosite, in an area ~1 x 6 cm2 on one edge of
the specimen. Crudely crystallized petewilliamsite, in isolated patches up to 3 mm in size and associated with
minor xanthiosite, is also found with predominant
aerugite elsewhere on the specimen. Subhedral equant grains are intimately
intergrown in 1 mm sized aggregates. Crystals are variable in colour from dark violet-red to dark brownish red, and the
streak is pale reddish brown to pale purplish brown. The lustre is vitreous and crystals are translucent
(MM 68.2.231-240).
Petewilliamsite from Johanngeorgenstadt -
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