Hohmannite is a rare, vibrant orange iron sulfate mineral that forms as a secondary product in the oxidation zones of sulfide ore deposits. It is most commonly found as microscopic tabular crystals or granular crusts, often associated with other rare sulfates in arid mining regions. Due to its solubility and sensitivity to hydration, specimens should be stored in a cool, dry environment to maintain their stability.
Is this hohmannite?
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 hohmannite with a known reference. Hohmannite sits at Mohs 3, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: yellow-orange.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous, brilliant.
- 4Match the color rangeCompare against the expected color range: brown, orange brown, reddish brown.
- 5Look at form & habitCrystal system: triclinic. Typical habit: tabular crystals, massive, granular, encrustations.
Often confused with
Hohmannite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Hohmannite leaves yellow-orange, Amarantite leaves lemon-yellow.
How to tell apart: Streak differs, so Hohmannite leaves yellow-orange, Metavoltine leaves brownish yellow; luster reads vitreous, brilliant on Hohmannite and resinous on Metavoltine.
How to tell apart: Streak differs, so Hohmannite leaves yellow-orange, Copiapite leaves pale yellow; luster reads vitreous, brilliant on Hohmannite and pearly on {010} on Copiapite.
Often found alongside hohmannite
Minerals reported to co-occur with hohmannite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Fe₂³⁺(SO₄)₂O·8H₂O
- Mohs hardness
- 3
- Density
- 2.255 g/cm³
- Streak
- Yellow-orange
- Luster
- Vitreous, brilliant
- Transparency
- Transparent to translucent
- Crystal system
- Triclinic
- Crystal habit
- Tabular crystals, massive, granular, encrustations
- Cleavage
- {010}, perfect; {110} and {110}, less perfect (referred to morphological axes; relation to X-ray axes uncertain)
- Rarity
- Rare
- Uses
- Collector
- Host rock
- An uncommon low-temperature precipitate in oxidized iron sulfide deposits
Where rockhounds find hohmannite
Classic worldwide localities
- Redington mine, Knoxville, Napa Co., California, USA
- Antofagasta, from near Caracoles, Sierra Gorda district, and at Alcaparrosa, near Cerritos Bayos, both southwest of Calama, Chile
- Quetena, west of Calama, Chile
- Chuquicamata, Chile
- Saghand, Yazd, Iran
- Plaka mine, near Laurium, Greece
Field-hunting tip
Where it forms: An uncommon low-temperature precipitate in oxidized iron sulfide deposits. If you start seeing metahohmannite, copiapite, amarantite in float, you are in the right ground. Typical habit: tabular crystals, massive, granular, encrustations. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify hohmannite?+
Where is hohmannite found?+
What rocks look like hohmannite?+
What minerals are found with hohmannite?+
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Find hohmannite on the map
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