A pyrite concretion, commonly known as a pyrite sun, is a flat, radiating crystalline growth that forms between layers of shale. Collectors seek it for its disc-like shape and metallic brassy luster, and it is often recovered by digging the spoil piles of old coal mines.
Is this pyrite concretion?
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 pyrite concretion with a known reference. Pyrite Concretion sits at Mohs 6-6.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Pyrite Concretion leaves a greenish-black streak.
- 3Read the lusterHold the specimen under a strong light. Pyrite Concretion typically shows a metallic luster.
- 4Match the color rangeCompare against the expected color range: brass-yellow.
- 5Look at form & habitCrystal system: cubic. Typical habit: radial fibrous disk.
Often confused with
Pyrite Concretion vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside pyrite concretion
Minerals reported to co-occur with pyrite concretion. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- FeS₂
- Mohs hardness
- 6-6.5
- Density
- 4.8-5.1 g/cm³
- Colors
- Streak
- Greenish-black
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Cubic
- Crystal habit
- Radial Fibrous Disk
- Cleavage
- None
- Rarity
- Uncommon
- Uses
- Collector, Decorative
- Host rock
- Sedimentary Shale and Coal Beds
Where rockhounds find pyrite concretion
3 mapped spotsClassic worldwide localities
- Sparta, Illinois
- Carbondale, Illinois
- Coal mines of the Illinois Basin
Field-hunting tip
Look in sedimentary shale and coal beds country, the host setting where pyrite concretion typically forms. If you start seeing shale, coal, sphalerite in float, you are in the right ground. Field specimens usually show a radial fibrous disk habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Kansas, Vermont, West Virginia. Start trip planning there.
More pyrite concretion photos
Common questions
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Find pyrite concretion on the map
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