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 May 18, 2026More igneous →

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Physical properties

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.

Other igneous specimens

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Blue Apatite

Fluorapatite (Ca5(PO4)3F)

mineral

Dark Igneous Rock (Likely Basalt or Diabase)

Basalt (extrusive igneous rock) or Diabase (intrusive igneous rock - also known as Dolerite), largely composed of plagioclase feldspar, pyroxene (augite), and sometimes olivine and amphibole. Exact mineralogy would require thin section analysis.

Igneous

Magnetite

Iron(II,III) oxide (Fe3O4)

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Blue Apatite

Apatite (Group), Ca5(PO4)3(F,Cl,OH)

mineral

Magnetite

Magnetite (Fe3O4)

mineral