Pigotite is a rare, poorly defined organic mineraloid occurring as brownish, alumina-rich deposits found in granite caves in Cornwall. It is essentially an organic material derived from the weathering of aluminum-bearing minerals by organic acids from vegetation.
Is this pigotite?
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 pigotite with a known reference. Pigotite sits at Mohs 1-2, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Pigotite leaves a yellowish-brown streak.
- 3Read the lusterHold the specimen under a strong light. Pigotite typically shows a dull luster.
- 4Match the color rangeCompare against the expected color range: brown, yellowish-brown.
- 5Look at form & habitCrystal system: amorphous. Typical habit: crusts, films, or stalactitic-like aggregates.
Often confused with
Pigotite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Limonite is the harder of the two (Mohs 4-5.5 vs. 1-2); luster reads dull on Pigotite and submetallic to earthy on Limonite.
How to tell apart: Iron Ore is the harder of the two (Mohs 5-6.5 vs. 1-2); streak differs, so Pigotite leaves yellowish-brown, Iron Ore leaves reddish-brown to black; luster reads dull on Pigotite and metallic to submetallic on Iron Ore.
Often found alongside pigotite
Minerals reported to co-occur with pigotite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Mohs hardness
- 1-2
- Colors
- Streak
- Yellowish-brown
- Luster
- Dull
- Transparency
- Opaque
- Crystal system
- Amorphous
- Crystal habit
- Crusts, Films, Or Stalactitic-like Aggregates
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Granite Cave Systems
- Typical price
- variable for rare organic specimens
Where rockhounds find pigotite
Classic worldwide localities
- Cornwall, England
Field-hunting tip
Look in granite cave systems country, the host setting where pigotite typically forms. If you start seeing quartz in float, you are in the right ground. Field specimens usually show a crusts, films, or stalactitic-like aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify pigotite?+
Where is pigotite found?+
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What minerals are found with pigotite?+
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Find pigotite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
