igneous

Basalt with Quartz Infill

Basalt (Mafic Extrusive Volcanic Rock)

Hardness: 6-7 Mohs; Color: Dark grey to black matrix with white mineral inclusion; Luster: Dull/Earthy (matrix), Vitreous (inclusion); Crystal Structure: Aphanitic (fine-grained); Specific Gravity: 2.8-3.0

Hardness: 6-7 Mohs
Color: Dark grey to black matrix with white mineral inclusion
Luster: Dull/Earthy (matrix), Vitreous (inclusion)

Identified May 28, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. The white patch is likely a secondary mineral deposit (like quartz or calcite) that filled a vesicle or crack after the rock cooled.

Uses & applications

Commonly used as aggregate in construction, road base, and concrete. Small river-worn specimens are popular for aquarium decor or landscaping.

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 extensively on the Moon and Mars.

Field identification & locations

Identify by its heavy weight, dark color, and fine-grained texture. To distinguish the white inclusion from calcite, a drop of vinegar can be used; if it bubbles, it is calcite; if not, it is likely quartz.

Other igneous specimens

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Blue Apatite

Fluorapatite (Ca5(PO4)3F)

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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

Dalmatian Jasper

Aplite with Arfvedsonite inclusions

igneous

Magnetite

Iron(II,III) oxide (Fe3O4)

mineral

Blue Apatite

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

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral