igneous

Red Porphyry

Porphyritic Andesite or Rhyolite

Hardness: 6-7 (Mohs scale); Color: Dark red to maroon groundmass with white or light-colored phenocrysts; Luster: Dull to sub-vitreous; Structure: Porphyritic (large crystals in a fine-grained matrix); Cleavage: None (conchoidal fracture).

Hardness: 6-7 (Mohs scale)
Luster: Dull to sub-vitreous

Identified March 26, 2026More igneous →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed through a two-stage cooling process of silica-rich magma; large crystals (phenocrysts) formed slowly at depth, followed by rapid cooling of the remaining melt near the surface. Often associated with volcanic arcs and Precambrian or Paleozoic geological ages.

Uses & applications

Used historically as a prestigious building material, for sculpture, and in modern times for high-end countertops, decorative paving, and crushed stone for road construction.

Geological facts

In antiquity, 'Imperial Porphyry' from Egypt was the most prestigious stone in the Roman Empire, reserved exclusively for the Emperor's use due to its purple-red color, which symbolized royalty.

Field identification & locations

Identify by looking for distinct, light-colored blocky crystals (usually feldspar) embedded in a uniform, fine-grained reddish background. Commonly found in glaciated regions as 'erratics' or near ancient volcanic sites. Collectors value well-worn river or beach cobbles for their aesthetic pattern.

Other igneous specimens

See all

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