To date (July 2023) there are no fewer than ten known minerals that have only As and S in their ideal formulae. They are:
orpiment and its paramorph
anorpiment, As2S3, As:S is 0.67
uzonite, As4S5, As:S is 0.80
alacranite, As8S9, As:S is 0.89
the paramorphs bonazziite,
realgar and pararealgar,
As4S4, As:S is 1.00
dimorphite and its paramorph
paradimorphite, As4S3, As:S is 1.33
duranusite, As4S, As:S is 4.00
Images
Formula: As8S9
Sulphide of arsenic, forms a series with
bonazziite
Crystal System: Monoclinic
Specific gravity: 3.43 measured, 3.43 calculated
Hardness: 1½
Streak: Yellow-orange
Colour: Orange to pale grey with rose-yellow internal reflections, yellow-orange in transmitted light
Luminescence: Non-fluorescent
Environments
Common associates of alacránite include chalcopyrite,
cinnabar, galena,
orpiment, pyrite,
realgar, sphalerite,
stibnite, sulphur and
uzonite
(Mindat).
Localities
At the Kateřina Coal Mine, Radvanice, Trutnov District, Hradec Králové Region, Czech Republic, alacránite occurs as
sublimates on a burning mine dump. Associated minerals include orpiment,
sulphur, an amorphous arsenic -
sulphur alloy, realgar,
pararealgar and anhydrite
(HOM).
There are two co-type Localities, the Alacrán mine, Alacrán, Pampa Larga mining district, Tierra Amarilla, Copiapó
Province, Atacama, Chile, and the Uzon Caldera, Kronotsky Reserve, Yelizovsky District, Kamchatka Krai, Russia.
At the Alacrán mine, Alacrán, Pampa Larga mining district, Tierra Amarilla, Copiapó Province, Atacama, Chile
(one of the type localities), alacránite occurs in hydrothermal arsenic -
sulphur veins. Associated minerals include
realgar, orpiment,
smithite, arsenic,
sulphur, stibnite,
pyrite, greigite,
arsenopyrite, arsenolamprite,
sphalerite, acanthite,
baryte, quartz and
calcite
(HOM).
At a Conical seamount in the Lihir Island area, New Ireland Province, Papua New Guinea, an
arsenic - sulphur mineral, purportedly
alacránite, formed at low temperatures in a polymetallic hydrothermal deposit on a submarine seamount. Associated
minerals include realgar, pyrite,
sphalerite, galena,
chalcopyrite and amorphous silica. The mineral occurs as subhedral to
euhedral tabular orange crystals that are transparent to translucent with a vitreous to resinous lustre. Crystals occur
both isolatedand as groupings within vugs and on matrix, and have a maximum length of 0.1 mm
(CM 39.3.809–818).
This mineral, however, was apparently As4S4, not As8S9, and it may be a new
mineral, not alacránite at all, so this locality is problematical.
At the Uzon Caldera, Kronotsky Reserve, Yelizovsky District, Kamchatka Krai, Russia, one of the type localities,
alacránite occurs in the condensation zone of a hydrothermal mercury -
antimony - arsenic system as cement in a
sandy gravel. Associated minerals include realgar,
orpiment, uzonite,
stibnite, cinnabar,
pyrite and sulphur
(HOM).
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