igneous

Basalt (with possible alteration or lichen)

Mafic volcanic rock (primarily Plagioclase and Pyroxene)

Hardness: 5-6 (Mohs); Color: Dark grey to black with light grey weathered patches; Luster: Dull/Sub-metallic; Structure: Fine-grained/Aphanitic; Specific Gravity: 2.8-3.0

Hardness: 5-6 (Mohs)
Color: Dark grey to black with light grey weathered patches
Luster: Dull/Sub-metallic

Identified May 31, 2026More igneous →

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Physical properties

Hardness: 5-6 (Mohs); Color: Dark grey to black with light grey weathered patches; Luster: Dull/Sub-metallic; Structure: Fine-grained/Aphanitic; 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. Common in oceanic crust and volcanic regions.

Uses & applications

Commonly used in construction as aggregate, in road building, as railroad ballast, and sometimes in stone carving or as high-strength insulation (mineral wool).

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 and Mars.

Field identification & locations

Identify by its dark color, high density, and fine-grained texture. It often breaks with a conchoidal or irregular fracture. Found in volcanic plateaus or near ocean ridges.

Other igneous specimens

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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

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