igneous

Basalt (River Pebble)

Extrusive Mafic Igneous Rock

Hardness: 6-7 on Mohs scale. Color: Dark grey to black, weathering to brown or green. Luster: Dull/Earthy (aphanitic). Crystal structure: Fine-grained/Microcrystalline. Specific gravity: 2.8–3.0.

Hardness: 6-7 on Mohs scale
Color: Dark grey to black, weathering to brown or green
Luster: Dull/Earthy (aphanitic)

Identified March 13, 2026More igneous →

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Physical properties

Hardness: 6-7 on Mohs scale. Color: Dark grey to black, weathering to brown or green. Luster: Dull/Earthy (aphanitic). Crystal structure: Fine-grained/Microcrystalline. 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. This specific specimen has been rounded and smoothed through fluvial erosion (water transport) over thousands of years.

Uses & applications

Commonly used as high-strength construction aggregate for roads and railroads, as a heat-retaining medium in 'hot stone' massage therapy, or as decorative landscaping 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 in abundance on the Moon and Mars.

Field identification & locations

Identify in the field by its heavy weight (high density), dark matte color, and lack of visible individual crystals. Look for smooth, rounded shapes in riverbeds or pitted 'vesicular' textures near volcanic sites.

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