Riotintoite is a very rare aluminum sulfate mineral typically found as a secondary mineral in mine waste environments. It usually forms delicate acicular or fibrous white crystal aggregates in association with other common sulfate minerals. Collectors often find it in crusts or efflorescences within heavily oxidized sulfide deposits.
Is this riotintoite?
4-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 riotintoite with a known reference. Riotintoite sits at Mohs 2.5, softer than the next harder reference, harder than the previous one.
- 2Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 3Match the color rangeCompare against the expected color range: colorless.
- 4Look at form & habitCrystal system: triclinic. Typical habit: acicular crystals, fibrous, crusts.
Often confused with
Riotintoite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside riotintoite
Minerals reported to co-occur with riotintoite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Al(SO₄)(OH)(H₂O)₃
- Mohs hardness
- 2.5
- Density
- 2.13 g/cm³
- Colors
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Triclinic
- Crystal habit
- Acicular crystals, fibrous, crusts
- Cleavage
- Good on {010}, {001}, and {201}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A secondary mineral in fissures cutting highly-altered volcanic breccia
Where rockhounds find riotintoite
Classic worldwide localities
- La Vendida mine (before 1990 known as the Rio Tinto mine), near Sierra Gorda, Antofagasta Region, Atacama Desert, Chile
Field-hunting tip
Where it forms: A secondary mineral in fissures cutting highly-altered volcanic breccia. If you start seeing vendidaite, eriochalcite, mg-rich aubertite in float, you are in the right ground. Typical habit: acicular crystals, fibrous, crusts. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify riotintoite?+
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What rocks look like riotintoite?+
What minerals are found with riotintoite?+
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Find riotintoite on the map
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