Alterite is a rare secondary sulfate mineral typically formed as a yellow-brown oxidation product of iron-bearing sulfides. It is often found as earthy crusts or pseudomorphs, making it challenging to identify visually without chemical analysis. Collectors typically seek it out as a component of gossan environments where it occurs alongside more common iron minerals.
Is this alterite?
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 alterite with a known reference. Alterite sits at Mohs 3.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Alterite leaves a yellow streak.
- 3Read the lusterHold the specimen under a strong light. Alterite typically shows a dull luster.
- 4Match the color rangeCompare against the expected color range: yellow, yellowish-brown, brown.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: pseudomorphs, massive, earthy.
Often confused with
Alterite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads dull on Alterite and vitreous on Jarosite.
How to tell apart: Streak differs, so Alterite leaves yellow, Limonite leaves yellowish-brown; luster reads dull on Alterite and submetallic to earthy on Limonite.
How to tell apart: Iron Ore is the harder of the two (Mohs 5-6.5 vs. 3.5); streak differs, so Alterite leaves yellow, Iron Ore leaves reddish-brown to black; luster reads dull on Alterite and metallic to submetallic on Iron Ore.
Often found alongside alterite
Minerals reported to co-occur with alterite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- KFe₃(OH)₆(SO₄)₂
- Mohs hardness
- 3.5
- Density
- 2.8-3.0 g/cm³
- Streak
- Yellow
- Luster
- Dull
- Transparency
- Opaque
- Crystal system
- Orthorhombic
- Crystal habit
- Pseudomorphs, Massive, Earthy
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Oxidized Hydrothermal Zones
- Typical price
- $20-150 for micromounts or small cabinet specimens
Where rockhounds find alterite
Classic worldwide localities
- Germany
- Czech Republic
- Kazakhstan
Field-hunting tip
Look in oxidized hydrothermal zones country, the host setting where alterite typically forms. If you start seeing jarosite, goethite, limonite in float, you are in the right ground. Field specimens usually show a pseudomorphs, massive, earthy habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find alterite on the map
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