igneous
Pyrite-bearing dark igneous rock, possibly basalt
Likely basalt or mafic volcanic rock with disseminated pyrite (FeS₂); identification is provisional from the photograph
AI-generated identification · may be incorrectDark gray-brown, fine-grained and dull to weakly metallic, with brassy-gold sulfide patches. Basalt typically has hardness 6–7 and specific gravity about 2.8–3.0; pyrite is harder (Mohs 6–6.5), cubic, and metallic.
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Physical properties
Dark gray-brown, fine-grained and dull to weakly metallic, with brassy-gold sulfide patches. Basalt typically has hardness 6–7 and specific gravity about 2.8–3.0; pyrite is harder (Mohs 6–6.5), cubic, and metallic.
Formation & geological history
Mafic lava cooled rapidly at or near Earth’s surface, with later hydrothermal fluids depositing pyrite in pores or fractures. The specimen’s geological age cannot be determined from the image.
Uses & applications
Basalt is used as aggregate, roadstone, and building stone; pyrite-bearing pieces are mainly collected as geological specimens. Pyrite is occasionally used for sulfur and mineral displays, but this material is unlikely to have jewelry value.
Geological facts
The gold-colored areas may be pyrite, though mica or weathered sulfides are also possible. A steel scratch test, streak test, and close inspection of crystal shape would improve identification.
Field identification & locations
Look for a dense dark matrix, tiny interlocking grains, and brassy cubic crystals; basalt commonly occurs in volcanic terrains worldwide. Pyrite leaves a greenish-black streak, unlike gold’s yellow streak.
