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?
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 riotintoite with a known reference. Riotintoite 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. Riotintoite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Riotintoite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, colorless.
- 5Look at form & habitCrystal system: orthorhombic. 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
- Al₂SO₄(OH)₄·3H₂O
- Mohs hardness
- 2
- Density
- 2.16 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Acicular Crystals, Fibrous, Crusts
- Cleavage
- Good
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Acid Mine Drainage Environments, Sulfate-rich Zones
- Typical price
- $50-200 for micro specimens
Where rockhounds find riotintoite
Classic worldwide localities
- Rio Tinto mine, Spain
- Tsumeb mine, Namibia
Field-hunting tip
Look in acid mine drainage environments, sulfate-rich zones country — that is the host setting where riotintoite typically forms. If you start seeing melanterite, jarosite, gypsum in float, you are in the right ground. Field specimens usually show a acicular crystals, fibrous, crusts habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify riotintoite?+
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Find riotintoite on the map
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