igneous

Basalt (River Stone)

Aphanitic Mafic Igneous Rock

Hardness: 6 (Mohs scale); Color: Dark grey to charcoal black; Luster: Dull to sub-metallic; Crystal structure: Microcrystalline (aphanitic); Cleavage: None; Specific gravity: 2.8–3.0

Hardness: 6 (Mohs scale)
Color: Dark grey to charcoal black
Luster: Dull to sub-metallic

Identified March 12, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs scale); Color: Dark grey to charcoal black; Luster: Dull to sub-metallic; Crystal structure: Microcrystalline (aphanitic); Cleavage: None; Specific gravity: 2.8–3.0

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. This specific specimen has been rounded by fluvial processes (water erosion) in a river or stream environment over thousands of years.

Uses & applications

Used in construction as aggregate, road base, and railroad ballast. Smooth river-worn basalt is highly valued for landscaping, decorative gardens, and hot stone massage therapy. It is also used as raw material for stone wool insulation.

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. Due to its density and thermal properties, it can hold heat for long periods, making it ideal for therapeutic uses.

Field identification & locations

Identify in the field by its heavy weight (high density), dark color, and fine-grained texture with no visible individual crystals. It is commonly found in volcanic regions, along ancient lava flows, and in riverbeds. Magnetism may sometimes be present due to magnetite inclusions.

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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