Torrecillasite is a rare arsenic-bearing mineral found in hyper-arid saline environments. It typically appears as colorless crusts or small aggregates within evaporite deposits in the Atacama region of Chile.
Is this torrecillasite?
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 torrecillasite with a known reference. Torrecillasite sits at Mohs 2.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: adamantine.
- 4Match the color rangeCompare against the expected color range: colorless.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: microcrystalline aggregates.
Often confused with
Torrecillasite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads adamantine on Torrecillasite and vitreous; pearly on cleavage surfaces on Claudetite.
How to tell apart: Torrecillasite is noticeably harder (Mohs 2.5 vs. 1.5); luster reads adamantine on Torrecillasite and vitreous to silky on Arsenolite.
Often found alongside torrecillasite
Minerals reported to co-occur with torrecillasite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Na(As,Sb)₄O₆Cl
- Mohs hardness
- 2.5
- Density
- 4.056 g/cm³
- Colors
- Streak
- White
- Luster
- Adamantine
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Microcrystalline aggregates
- Cleavage
- None observed, however likely on {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A secondary mineral formed by the oxidation of native As and As-bearing minerals in hydrothermal veins followed by later alteration by saline fluids derived from evaporating meteoric water under hyperarid conditions
Where rockhounds find torrecillasite
Classic worldwide localities
- Torrecillas mine, Torrecillas Hill, northern Atacama Desert, Iquique Province, Tarapacá Region, Chile
Field-hunting tip
Where it forms: A secondary mineral formed by the oxidation of native As and As-bearing minerals in hydrothermal veins followed by later alteration by saline fluids derived from evaporating meteoric water under hyperarid conditions. If you start seeing anhydrite, cinnabar, gypsum in float, you are in the right ground. Typical habit: microcrystalline aggregates. Train your eye for that shape before scanning the outcrop.
Common questions
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Find torrecillasite on the map
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