igneous

Basalt (Water-worn pebble)

Mafic Igneous Rock (primarily Plagioclase feldspar and Pyroxene)

Hardness: 5-6 Mohs; Color: Dark grey to charcoal; Luster: Dull/Matte; Crystal structure: Aphanitic (fine-grained, crystals not visible to eye); Specific gravity: 2.8-3.0; Cleavage: None (conchoidal fracture).

Hardness: 5-6 Mohs
Color: Dark grey to charcoal
Luster: Dull/Matte

Identified March 9, 2026More igneous →

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Physical properties

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 shows rounding and smoothing indicative of fluvial or coastal erosion (water-worn).

Uses & applications

Used extensively in construction as aggregate (crushed stone), for paving, and in the manufacturing of stone wool insulation. Dense specimens are also used for '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 extensively on the Moon (the dark 'Maria') and Mars.

Field identification & locations

Identify by its dark color, heavy weight for its size, and lack of visible crystals. Commonly found in volcanic regions, riverbeds downstream from volcanic plateaus, and along beaches. Collectors value specimens with unique shapes or vesicles.

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

Magnetite

Iron(II,III) oxide (Fe3O4)

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Blue Apatite

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

mineral

Magnetite

Magnetite (Fe3O4)

mineral