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?
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 alterite with a known reference. Alterite sits at Mohs 3.5, softer than the next harder reference, harder than the previous one.
- 2Read the lusterHold the specimen under a strong light. Luster: dull.
- 3Match the color rangeCompare against the expected color range: yellow, yellowish-brown, brown.
- 4Look at form & habitCrystal system: monoclinic. 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 subadamantine to vitreous, resinous on fractures on Jarosite.
How to tell apart: Luster reads dull on Alterite and submetallic to earthy on Limonite.
How to tell apart: Goethite is the harder of the two (Mohs 5-5.5 vs. 3.5); luster reads dull on Alterite and imperfect adamantine metallic to dull earthy; silky when fibrous on Goethite.
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
- Zn₂Fe³⁺₄(SO₄)₄(C₂O₄)₂(OH)₄·17H₂O
- Mohs hardness
- 3.5
- Density
- 2.8-3.0 g/cm³
- Luster
- Dull
- Transparency
- Opaque
- Crystal system
- Monoclinic
- Crystal habit
- Pseudomorphs, massive, earthy
- Rarity
- Rare
- Uses
- Collector
- Host rock
- oxidized hydrothermal zones
Where rockhounds find alterite
Classic worldwide localities
- Near the Cliff Dwellers Lodge, Vermillion Cliffs, Coconino Co., Arizona, USA
Field-hunting tip
Where it forms: oxidized hydrothermal zones. If you start seeing jarosite, goethite, limonite in float, you are in the right ground. Typical habit: pseudomorphs, massive, earthy. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify alterite?+
Where is alterite found?+
What rocks look like alterite?+
What minerals are found with alterite?+
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Find alterite on the map
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