Antofagastaite is a rare hydrated sodium-calcium sulfate mineral typically found as delicate, needle-like or fibrous crystal aggregates in arid evaporite settings. Collectors look for these fragile formations within the hyper-arid regions of the Atacama Desert in Chile, where it occurs as a secondary precipitate.
Is this antofagastaite?
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 antofagastaite with a known reference. Antofagastaite sits at Mohs 2, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Antofagastaite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Antofagastaite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, colorless.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: fibrous, acicular, prismatic.
Often confused with
Antofagastaite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside antofagastaite
Minerals reported to co-occur with antofagastaite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Na₂Ca(SO₄)₂·2H₂O
- Mohs hardness
- 2
- Density
- 2.19 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Fibrous, Acicular, Prismatic
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Evaporite Deposits
- Typical price
- $50-300 per specimen
Where rockhounds find antofagastaite
Classic worldwide localities
- Antofagasta, Chile
Field-hunting tip
Look in evaporite deposits country, the host setting where antofagastaite typically forms. If you start seeing halite, anhydrite, gypsum in float, you are in the right ground. Field specimens usually show a fibrous, acicular, prismatic habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify antofagastaite?+
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Find antofagastaite on the map
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