igneous

Basalt with Quartz/Feldspar Inclusion

Basalt (containing Silicate minerals such as SiO2 and (Ca,Na)(Al,Si)4O8)

Hardness: 5-7 (Mohs scale); Color: Dark grey to black matrix with lighter cream or brownish inclusions; Luster: Dull to sub-vitreous; Structure: Aphanitic (fine-grained) with weathered surfaces; Specific Gravity: 2.8–3.0

Hardness: 5-7 (Mohs scale)
Luster: Dull to sub-vitreous

Identified March 8, 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 near the Earth's surface. The lighter patches represent secondary mineral growth or xenoliths trapped during the cooling of volcanic flows, common in Cenozoic era deposits.

Uses & applications

Common basalt is used extensively in construction as aggregate for roads and concrete. Specimens with unique inclusions or wear patterns are primarily of interest to amateur rock collectors and students for educational purposes.

Geological facts

Basalt is the most common rock in Earth's crust and makes up most of the ocean floor. It is also found on the Moon (the dark lunar maria) and Mars.

Field identification & locations

Identify in the field by its high density, dark color, and fine texture. Frequently found in volcanic fields, riverbeds, and as coastal pebbles. Collectors should look for unique grain patterns or high-contrast inclusions like the one pictured.

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