Epidosite Identification Guide
Identify epidosite, the distinctive pistachio-green quartz-epidote rock, using color, hardness, and texture in the field.
Read the full Epidosite encyclopedia entry →
What Epidosite Looks Like
Epidosite is a metasomatic/metamorphic rock composed mainly of epidote and quartz, formed where hydrothermal fluids altered basalt or other mafic rock. Its appearance is unmistakable once known.
- Color: bright yellowish-green to pistachio or olive green (epidote), streaked or speckled with white to gray (quartz).
- Luster: vitreous; epidote can look slightly glassy to silky.
- Texture: granular, sometimes veined or patchy; can be fine to medium grained.
- Form: massive rock, not single crystals; often occurs as veins, pods, and replacement zones.
Step-by-Step Field-ID Checklist
- Note the green. A strong, slightly yellowish "pistachio" green over much of the rock points to epidote.
- Spot the quartz. Look for glassy white-to-gray patches and veinlets intergrown with the green.
- Hardness check. It scratches glass; both epidote (6-7) and quartz (7) are hard. Soft green minerals (chlorite, serpentine) do not qualify.
- Look at setting. Found in altered volcanics, especially old ocean-floor basalts and shear zones.
- Check for heft. Epidosite is moderately dense and feels solid.
Key Diagnostic Tests
- Mohs hardness: ~6-7 overall (epidote 6-7, quartz 7); will not be scratched by a steel knife.
- Streak: white to grayish.
- Cleavage/fracture: epidote has one good cleavage but the rock breaks with uneven fracture.
- Specific gravity: ~3.2-3.4, heavier than plain quartzite because of the epidote.
- Acid: no fizz (distinguishes it from green-stained carbonate rocks).
- No magnetism.
Common Look-Alikes and How to Tell Them Apart
- Unakite: a granite containing pink feldspar plus green epidote; epidosite lacks the pink feldspar and is dominantly green-and-quartz.
- Greenstone/serpentinite: softer, can be scratched by a knife, often waxy or soapy feel; epidosite is hard and glassy.
- Green quartzite/aventurine: color is paler and more uniform, lacks the granular epidote masses; lower density.
- Chlorite schist/greenschist: foliated and soft, flakes easily, unlike the hard granular epidosite.
Where It Is Typically Found
Epidosite forms in hydrothermally altered oceanic crust (ophiolites) and volcanic terranes worldwide, including the Troodos ophiolite (Cyprus), the Alps, Norway, Scotland, and many western US greenstone belts. It is common in epidote-rich veins cutting basalt and diabase.
Frequently asked questions
What is epidosite made of?
Epidosite is composed predominantly of epidote and quartz, with minor amounts of feldspar, titanite, or magnetite. It forms when hot fluids alter basaltic or mafic rock, concentrating epidote.
How can you tell epidosite from unakite?
Unakite combines pink feldspar with green epidote and gray quartz, giving a pink-and-green look. Epidosite is dominated by green epidote and quartz with little to no pink feldspar.
Is epidosite hard?
Yes. With epidote at 6-7 and quartz at 7 on the Mohs scale, epidosite scratches glass and resists a steel knife, unlike softer green rocks such as serpentinite or chlorite schist.
What color is epidosite?
A characteristic bright yellowish-green, often called pistachio or olive green, mottled and veined with white to gray quartz.
Epidosite identified by the community
Recent Epidosite specimens identified with Rock Identifier.
