igneous

Basalt with Olivine (Peridot)

Basalt containing (Mg,Fe)2SiO4

Hardness: 6-7 (Olivine), 5.5-6 (Basalt). Color: Dark gray to black matrix with olive-green phenocrysts. Luster: Vitreous in crystals, dull in matrix. Crystal structure: Orthorhombic olivine.

Hardness: 6-7 (Olivine), 5
Color: Dark gray to black matrix with olive-green phenocrysts
Luster: Vitreous in crystals, dull in matrix

Identified May 28, 2026More igneous →

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Physical properties

Hardness: 6-7 (Olivine), 5.5-6 (Basalt). Color: Dark gray to black matrix with olive-green phenocrysts. Luster: Vitreous in crystals, dull in matrix. Crystal structure: Orthorhombic olivine.

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. Common in oceanic crust and volcanic islands.

Uses & applications

Basalt is used in road base, railroad ballast, and concrete aggregate. Large olivine crystals (Peridot) are used in jewelry.

Geological facts

Olivine is one of the first minerals to crystallize from a cooling magma and is a major component of the Earth's upper mantle.

Field identification & locations

Check for small, glassy green grains embedded in a dense, dark, fine-grained rock. Often found in volcanic fields like those in Hawaii, Arizona, or Iceland.

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

Dalmatian Jasper

Aplite with Arfvedsonite inclusions

igneous

Magnetite

Iron(II,III) oxide (Fe3O4)

mineral

Blue Apatite

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

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral