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 — 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 — 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 — that is 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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