Penberthycroftite is a rare arsenate mineral originally discovered in the historic mines of Cornwall, England. It typically appears as thin, yellowish to brownish-orange coatings or crusts associated with other secondary arsenic minerals in oxidized vein outcrops.
Is this penberthycroftite?
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 penberthycroftite with a known reference. Penberthycroftite 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. Penberthycroftite leaves a yellow streak.
- 3Read the lusterHold the specimen under a strong light. Penberthycroftite typically shows a resinous luster.
- 4Match the color rangeCompare against the expected color range: yellow, orange, brown.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: microcrystalline, crusts, or massive.
Often confused with
Penberthycroftite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Penberthycroftite leaves yellow, Descloizite leaves orange to brownish-red; luster reads resinous on Penberthycroftite and greasy to adamantine on Descloizite.
How to tell apart: Streak differs — Penberthycroftite leaves yellow, Mimetite leaves white; luster reads resinous on Penberthycroftite and adamantine on Mimetite.
Often found alongside penberthycroftite
Minerals reported to co-occur with penberthycroftite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Zn₂Fe³⁺(AsO₄)(OH)₂·H₂O
- Mohs hardness
- 3.5
- Density
- 6.05 g/cm³
- Streak
- Yellow
- Luster
- Resinous
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Microcrystalline, Crusts, Or Massive
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Hydrothermal Veins in Oxidized Base Metal Deposits
- Typical price
- $50-300 per specimen
Where rockhounds find penberthycroftite
Classic worldwide localities
- Penberthy Croft Mine, Cornwall, England
- Tsumeb Mine, Namibia
Field-hunting tip
Look in hydrothermal veins in oxidized base metal deposits country — that is the host setting where penberthycroftite typically forms. If you start seeing goethite, mimetite, cornwallite in float, you are in the right ground. Field specimens usually show a microcrystalline, crusts, or massive habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find penberthycroftite on the map
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