igneous

Basalt with Peridotite (Olivine) Xenolith

Olivine-rich Peridotite (Dunite) xenolith in Vesicular Basalt; chemical formula (Mg,Fe)2SiO4

Hardness: 6.5-7 (Mohs scale for olivine). Color: Olive green to yellowish-green crystals embedded in a dark grey to black fine-grained or vesicular matrix. Luster: Vitreous (glassy) for the green crystals, dull for the matrix. Crystal structure: Orthorhombic.

Hardness: 6

Identified March 21, 2026More igneous →

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Physical properties

Formation & geological history

Formed at great depths in the Earth's mantle and carried to the surface by rapidly rising basaltic magma during volcanic eruptions. Age can vary from thousands to millions of years depending on the specific volcanic site.

Uses & applications

Primarily used as geological specimens for research and collecting. Gem-quality olivine (Peridot) is used in jewelry. The surrounding basalt is commonly used in road construction and as aggregate.

Geological facts

These are known as 'xenoliths,' which literally means 'foreign rocks.' They are essentially pieces of the Earth's upper mantle that were trapped in lava and brought to the surface before they could melt.

Field identification & locations

Identify in the field by looking for distinct green, translucent to transparent crystal clusters inside dark volcanic basalt. Common locations include volcanic fields in Arizona (Peridot Mesa), Hawaii, and the Canary Islands.

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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.

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