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, so 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, so 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, 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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