Auriacusite is a rare copper iron phosphate mineral typically found as small, platy yellow to brownish-yellow crystals. It is primarily known from specific hydrothermal vein deposits such as the Grube Clara in the Black Forest of Germany.
Is this auriacusite?
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 auriacusite with a known reference. Auriacusite 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: brownish yellow.
- 3Read the lusterHold the specimen under a strong light. Luster: silky.
- 4Match the color rangeCompare against the expected color range: brownish golden-yellow.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: platy crystals.
Often confused with
Auriacusite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Auriacusite leaves brownish yellow, Ludjibaite leaves pale blue to white; luster reads silky on Auriacusite and vitreous on Ludjibaite.
How to tell apart: Pseudomalachite is the harder of the two (Mohs 4.5-5 vs. ~3); streak differs, so Auriacusite leaves brownish yellow, Pseudomalachite leaves pale green to pale bluish green; luster reads silky on Auriacusite and vitreous to resinous on Pseudomalachite.
Often found alongside auriacusite
Minerals reported to co-occur with auriacusite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- FeCu(AsO₄)O
- Mohs hardness
- ~3
- Density
- 4.447 g/cm³
- Colors
- Brownish golden-yellow
- Streak
- Brownish yellow
- Luster
- Silky
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Platy crystals
- Cleavage
- Perfect on {010}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A secondary mineral in the weathering zone of a polymetallic sulfarsenide deposit
Where rockhounds find auriacusite
Classic worldwide localities
- Black Pine mine, 14.5 km NW of Philipsburg, Granite County, Montana, USA
Field-hunting tip
Where it forms: A secondary mineral in the weathering zone of a polymetallic sulfarsenide deposit. If you start seeing segnitite, brochantite, malachite in float, you are in the right ground. Typical habit: platy crystals. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify auriacusite?+
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Find auriacusite on the map
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