Hisingerite is an amorphous, iron-rich silicate mineral that commonly occurs as a secondary alteration product in igneous rocks or sulfide veins. It is typically found in massive, resinous, dark brown to black crusts that can be easily mistaken for other iron-rich amorphous minerals like allophane or limonite.
Is this hisingerite?
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 hisingerite with a known reference. Hisingerite sits at Mohs 2.5-3, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: yellowish brown.
- 3Read the lusterHold the specimen under a strong light. Luster: resinous, vitreous, greasy.
- 4Match the color rangeCompare against the expected color range: black, brownish black.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: acicular, compact, massive.
Often confused with
Hisingerite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Hisingerite leaves yellowish brown, Allophane leaves white; luster reads resinous, vitreous, greasy on Hisingerite and vitreous to earthy, waxy on Allophane.
How to tell apart: Limonite is the harder of the two (Mohs 4-5.5 vs. 2.5-3); streak differs, so Hisingerite leaves yellowish brown, Limonite leaves yellowish-brown; luster reads resinous, vitreous, greasy on Hisingerite and submetallic to earthy on Limonite.
Often found alongside hisingerite
Minerals reported to co-occur with hisingerite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Fe³⁺₂Si₂O₅(OH)₄·2H₂O
- Mohs hardness
- 2.5-3
- Density
- 2.43-2.67 g/cm³
- Colors
- Streak
- Yellowish brown
- Luster
- Resinous, vitreous, greasy
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
- Crystal habit
- Acicular, compact, massive
- Cleavage
- None
- Rarity
- Uncommon
- Uses
- Collector, Scientific research
- Host rock
- A secondary mineral, formed from the weathering, or late-stage deuteric or hydrothermal alteration, of iron-bearing silicates or sulfides; by late-stage hydrothermal activity during sulfide ore deposition
Where rockhounds find hisingerite
Classic worldwide localities
- Hibbing district, St. Louis Co., Minnesota, USA
- Castle Dome mine, Gila Co., and on the Mildren and Steppe claims, Cababi district, Pima Co., Arizona, USA
- Gap Nickel mine, Lancaster Co., Pennsylvania, USA
- Riddarhyttan, Västmanland, and Långban, Värmland, Sweden
- Fagul Cetatii, Balan, Romania
- Salberg, Norway
Field-hunting tip
Where it forms: A secondary mineral, formed from the weathering, or late-stage deuteric or hydrothermal alteration, of iron-bearing silicates or sulfides; by late-stage hydrothermal activity during sulfide ore deposition. If you start seeing olivine, pyroxene, pyrite in float, you are in the right ground. Typical habit: acicular, compact, massive. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify hisingerite?+
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Find hisingerite on the map
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