Alacránite is a rare arsenic sulfide mineral typically found in epithermal gold-silver deposits. Collectors should look for its distinctive orange-red hue in hydrothermal vein assemblages, where it often forms as a secondary alteration product of realgar.
Is this alacránite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch alacránite with a known reference. Alacránite sits at Mohs 1.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: yellow-orange.
- 3Read the lusterHold the specimen under a strong light. Luster: adamantine, vitreous, resinous, greasy.
- 4Match the color rangeCompare against the expected color range: red, orange yellow.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: equant grains, euhedral crystals.
Often confused with
Alacránite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Alacránite leaves yellow-orange, Realgar leaves red-orange to red; luster reads adamantine, vitreous, resinous, greasy on Alacránite and resinous to greasy on Realgar.
How to tell apart: Streak differs, so Alacránite leaves yellow-orange, Orpiment leaves pale lemon-yellow; luster reads adamantine, vitreous, resinous, greasy on Alacránite and resinous, pearly on cleavage surface on Orpiment.
Often found alongside alacránite
Minerals reported to co-occur with alacránite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- As₈S₉
- Mohs hardness
- 1.5
- Density
- 3.43 g/cm³
- Colors
- Streak
- Yellow-orange
- Luster
- Adamantine, vitreous, resinous, greasy
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
- Crystal habit
- Equant grains, euhedral crystals
- Cleavage
- Imperfect on {100}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In hydrothermal As-S veins (Alacrán mine, Chile); in the condensation zone of a hydrothermal Hg-Sb-As system as cement in a sandy gravel (Uzon caldera, Russia)
Where rockhounds find alacránite
Classic worldwide localities
- Alacrán mine, Pampa Larga district, Copiapó, Chile
- Uzon caldera, Kamchatka, Russia
- Tiefengraben, Reinerzau, Black Forest, Germany
- Conical Seamount, ten km south-southeast of Lihir Island, Papua New Guinea
- Nishinomaki mine, Gunma Prefecture, Japan
- Burning dumps of the Kateřina mine, Radvanice, Czech Republic
Field-hunting tip
Where it forms: In hydrothermal As-S veins (Alacrán mine, Chile); in the condensation zone of a hydrothermal Hg-Sb-As system as cement in a sandy gravel (Uzon caldera, Russia). If you start seeing realgar, orpiment, smithite in float, you are in the right ground. Typical habit: equant grains, euhedral crystals. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify alacránite?+
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What rocks look like alacránite?+
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Find alacránite on the map
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