igneous

Basalt Pebble

Basalt (Aphanitic Mafic Igneous Rock)

Hardness: 6 on Mohs scale; Color: Dark grey to black (weathered to light grey); Luster: Dull/Earthy; Crystal Structure: Very fine-grained (aphanitic) microcrystalline; Cleavage: None; Specific Gravity: 2.8–3.0

Hardness: 6 on Mohs scale
Color: Dark grey to black (weathered to light grey)
Luster: Dull/Earthy

Identified March 15, 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 from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the surface of a terrestrial planet or a moon. This specimen shows river or beach erosion (rounding) indicating it was transported by water long after its initial volcanic formation.

Uses & applications

Used extensively in construction as aggregate (crushed stone) for roads, railroad ballast, and concrete. In polished form, it is used for decorative landscaping and massage stones.

Geological facts

Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It is also found on the Moon, Mars, and Venus.

Field identification & locations

Identify in the field by its dark interior, weight (denser than granite), and lack of visible large crystals. Commonly found in volcanic fields, riverbeds draining volcanic areas, and coastal regions with basaltic cliffs.

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

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