igneous

Basalt (Porphyritic)

Porphyritic Basalt

Hardness: 6.0; Color: Dark grey to black with light-colored phenocrysts; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic groundmass with visible crystals; Specific Gravity: 2.8–3.0.

Hardness: 6
Color: Dark grey to black with light-colored phenocrysts
Luster: Dull to sub-metallic

Identified May 28, 2026More igneous →

Identify your own rocks.

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

App Store Google Play

Physical properties

Hardness: 6.0; Color: Dark grey to black with light-colored phenocrysts; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic groundmass with visible crystals; Specific Gravity: 2.8–3.0.

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. The visible spots (phenocrysts) formed deeper underground before the final eruption.

Uses & applications

Commonly used in construction as aggregate, for road base, and in the production of stone wool insulation.

Geological facts

Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor, as well as the surfaces of the Moon and Mars.

Field identification & locations

Identify by its heavy weight, dark color, and the presence of small, distinct crystals embedded in a fine-grained matrix. Often found in volcanic regions or riverbeds downstream from volcanic sources.

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