igneous
Porphyritic Rhyolite (Birdseye Rhyolite)
Rhyolite (Porphyritic texture)
Hardness: 6-7 Mohs; Color: Tan or cream matrix with reddish-brown phenocrysts; Luster: Dull/Earthy; Crystal structure: Aphanitic matrix with visible large crystals; Cleavage: None; Specific Gravity: 2.4-2.6
- Hardness
- 6-7 Mohs
- Color
- Tan or cream matrix with reddish-brown phenocrysts
- Luster
- Dull/Earthy
Identified More igneous →
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Physical properties
Hardness: 6-7 Mohs; Color: Tan or cream matrix with reddish-brown phenocrysts; Luster: Dull/Earthy; Crystal structure: Aphanitic matrix with visible large crystals; Cleavage: None; Specific Gravity: 2.4-2.6
Formation & geological history
Formed through rapid cooling of silica-rich volcanic lava at or near the Earth's surface, where larger phenocrysts (often feldspar or quartz) were already formed before the final eruption.
Uses & applications
Used primarily as decorative stone, lapidary material for cabochons, and in landscape architecture.
Geological facts
Also known as 'Rainforest Jasper' or 'Birdseye Rhyolite' in the gem trade, though strictly it is an igneous rock rather than a true jasper.
Field identification & locations
Identify by looking for 'eyes' or distinct spots of color embedded in a fine-grained matrix. Often found in volcanic regions like the American Southwest or Australia.
