RocksdayRocksday #3 · October 24, 2026
The answer was Pyrite
Brassy iron sulfide famous as 'fool's gold'. It often forms startlingly perfect cubes with fine parallel lines on the faces.
The clues
- Type
- Mineral
- Color & luster
- Gold · Metallic
- Mohs hardness
- 6–6.5
- Crystal system
- Cubic
- Found in
- Navajún, Spain; Huanzala, Peru
How to recognize pyrite
- Pale brass-yellow metallic color.
- Streak is greenish black, not gold.
- Hard and brittle — it shatters rather than flattens when struck.
- Cubes with striated faces, or twelve-sided pyritohedrons.
Did you know? The name comes from Greek pyr, 'fire' — pyrite throws sparks when struck with steel.