igneous

Epidote in Basalt

Epidotized Basalt (Ca2(Al2,Fe)(SiO4)(Si2O7)O(OH) in Mafic Igneous Host)

Hardness: 6-7 (Mohs scale); Color: Pistachio green to yellowish-green (epidote) against dark grey/black (basalt); Luster: Vitreous to dull; Crystal structure: Monoclinic; Cleavage: Perfect in one direction for epidote crystals.

Hardness: 6-7 (Mohs scale)
Luster: Vitreous to dull

Identified March 24, 2026More igneous →

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Physical properties

Formation & geological history

Formed via hydrothermal alteration or low-grade metamorphism (greenschist facies) where hot, mineral-rich fluids react with calcium-rich plagioclase feldspar and pyroxene within basaltic rock.

Uses & applications

Primarily used as a decorative stone, semi-precious gemstone (Unakite variety if with pink feldspar), or as industrial crushed stone and road aggregate.

Geological facts

Epidote gets its name from the Greek word 'epidosis' meaning 'addition', referring to the crystal's base having one side longer than the other. The green color is a direct result of iron content within the mineral structure.

Field identification & locations

Identify in the field by looking for the distinctive 'pistachio green' color in veins or patches within dark, fine-grained volcanic rocks. Commonly found in areas with past volcanic activity like Lake Superior (USA), Norway, and the Alps.

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

Blue Apatite

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

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Magnetite

Magnetite (Fe3O4)

mineral