igneous

Basalt (River or Beach Pebble)

Basalt (Mafic Extrusive Igneous Rock)

Hardness: 5-6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-metallic (when wet); Crystal Structure: Aphanitic (fine-grained/microscopic); Cleavage: None; Specific Gravity: 2.8-3.0.

Hardness: 5-6 (Mohs scale)
Color: Dark grey to black
Luster: Dull to sub-metallic (when wet)

Identified March 28, 2026More igneous →

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Physical properties

Hardness: 5-6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-metallic (when wet); Crystal Structure: Aphanitic (fine-grained/microscopic); 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 near the Earth's surface. This specific specimen has been subsequentely rounded and smoothed by water erosion (fluvial or marine movement) over hundreds to thousands of years.

Uses & applications

Used extensively in construction as crushed stone for road base, concrete aggregate, and railroad ballast. Exceptionally smooth specimens are used in decorative landscaping and hot stone massage therapy.

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, where it forms the dark 'seas' known as lunar maria.

Field identification & locations

Identify in the field by its high density, dark color, and lack of visible large crystal grains. It is non-reactive to acid (distinguishing it from limestone). Commonly found in volcanic regions, riverbeds, and along tectonic plate boundaries.

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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

Magnetite

Iron(II,III) oxide (Fe3O4)

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

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Blue Apatite

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

mineral

Magnetite

Magnetite (Fe3O4)

mineral