igneous

Basalt with Quartz/Calcite Vein

Basalt (Mafic Volcanic Rock with secondary mineralization)

Hardness: 5-6 (matrix); Color: Dark brown to charcoal gray with a tan/white vein; Luster: Dull/Earthy; Crystal Structure: Aphanitic (fine-grained) matrix with a secondary crystalline vein; Cleavage: None (conchoidal fracture in matrix).

Hardness: 5-6 (matrix)
Color: Dark brown to charcoal gray with a tan/white vein
Luster: Dull/Earthy

Identified January 12, 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

Basalt forms from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. This specimen features a secondary mineral vein (likely quartz or calcite) deposited by hydrothermal fluids moving through cracks in the rock long after the basalt solidified.

Uses & applications

Basalt is widely used in construction as aggregate for roads, railroad ballast, and in the production of high-strength stone wool insulation. Collectors value specimens with distinct mineral veining for display.

Geological facts

Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. The dark color is due to the presence of pyroxene and calcium-rich plagioclase feldspar.

Field identification & locations

Identify in the field by its heavy weight (high specific gravity), dark color, and fine-grained texture. Look for the distinct contrasting 'stripe' of the vein. Common in volcanic regions such as the Pacific Northwest, Hawaii, and Iceland.

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