metamorphic
Pyrite in Slate
Iron Sulfide (FeS2) in Slate host matrix
Hardness: 6-6.5 (Pyrite), 2.5-4 (Slate host); Color: Brass-yellow to golden metallic crystals on dark gray to black host; Luster: Metallic (crystals) to dull/earthy (matrix); Crystal Structure: Cubic/Pyritohedral; Cleavage: Poor/Invisible
- Hardness
- 6-6
- Luster
- Metallic (crystals) to dull/earthy (matrix)
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Physical properties
Hardness: 6-6.5 (Pyrite), 2.5-4 (Slate host); Color: Brass-yellow to golden metallic crystals on dark gray to black host; Luster: Metallic (crystals) to dull/earthy (matrix); Crystal Structure: Cubic/Pyritohedral; Cleavage: Poor/Invisible
Formation & geological history
Formed through low-grade regional metamorphism of shale containing organic matter and iron oxides, combined with hydrothermal fluids rich in sulfur, leading to the growth of pyrite crystals within the slate matrix.
Uses & applications
Educational geological specimen, decorative rock collection piece, historically used as a source of sulfur and iron ore.
Geological facts
Pyrite is famously known as 'Fool's Gold' due to its metallic luster and brassy yellow color which often tricked novice prospectors. When struck against steel, pyrite produces sparks.
Field identification & locations
Identified by the contrast of sparkling golden metallic crystals against a fine-grained, dark, foliated metamorphic rock matrix. Common in slate-producing regions worldwide such as Wales, Spain, and North America.
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