igneous

Basalt

Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to matte; Structure: Aphanitic (fine-grained); Specific Gravity: 2.8–3.0; Composition: Plagioclase feldspar and pyroxene.

Hardness: 6 (Mohs scale)
Color: Dark grey to black
Luster: Dull to matte

Identified May 9, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to matte; Structure: Aphanitic (fine-grained); Specific Gravity: 2.8–3.0; Composition: Plagioclase feldspar and pyroxene.

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. It is the most common volcanic rock on Earth, often found in oceanic crust and lava flows.

Uses & applications

Extensively used in construction for road base, concrete aggregate, railroad ballast, and dimension stone for pavers or countertops.

Geological facts

Basalt also makes up most of the ocean floors and is found on the Moon and Mars. It can form unique hexagonal columns during cooling, such as those at the Giant's Causeway.

Field identification & locations

Identify by its heavy weight (high density), dark color, and lack of visible crystals to the naked eye. Commonly found in volcanic regions and shorelines.

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