Eulysite Identification Guide
Identify eulysite, a rare iron-rich metamorphic rock built on fayalite and iron silicates, by its dark dense character and mineral associations.
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What Eulysite Looks Like
Eulysite is a rare, iron-rich metamorphic rock characterized by fayalite (iron-olivine) together with iron-rich pyroxene, amphibole, and garnet (almandine). It typically represents metamorphosed iron-rich (often manganese-bearing) sediments.
- Color: dark gray, brownish, to greenish-black, often with rusty weathering.
- Texture: granular, medium to coarse grained, sometimes with visible garnet porphyroblasts.
- Minerals: fayalite, ferro-hypersthene/iron pyroxene, grunerite/iron amphibole, almandine garnet, magnetite, sometimes manganese silicates.
- Form: massive lenses and bands within high-grade metamorphic terranes.
Step-by-Step Field-ID Checklist
- Note the heft. Eulysite is dense because of its iron-rich minerals.
- Look for garnet. Dark red almandine porphyroblasts in a dark matrix are common.
- Check weathering color. A rusty/limonitic stain hints at high iron content.
- Confirm it is metamorphic. Granular interlocking texture, sometimes faintly banded, found in gneiss/granulite terranes.
- Hardness. Constituent silicates scratch glass (6.5-7.5 for olivine/garnet).
Key Diagnostic Tests
- Mohs hardness: ~6.5-7.5 for the main silicates; will not be scratched by a knife.
- No acid fizz (it is a silicate rock).
- Specific gravity: high (~3.5-4.0+), reflecting fayalite, garnet, and magnetite.
- Magnetism: often magnetic due to magnetite content.
- Cleavage: seen in individual pyroxene/amphibole grains; rock fractures unevenly.
Common Look-Alikes and How to Tell Them Apart
- Eclogite: also dense and garnet-bearing, but eclogite pairs red garnet with green omphacite (sodic pyroxene); eulysite is dominated by iron olivine and iron silicates, not green omphacite.
- Garnet amphibolite/granulite: less extreme iron enrichment; eulysite is distinctly fayalite-rich and denser.
- Skarn/iron formation: banded iron formation is layered hematite/magnetite-chert and lacks fayalite porphyroblastic texture.
- Peridotite: olivine-rich but magnesian (green), igneous, and lacks abundant almandine garnet.
Where It Is Typically Found
Eulysite occurs in high-grade (granulite-facies) metamorphic terranes derived from iron-rich protoliths. Classic occurrences are in Sweden (the type area, Tunaberg/Mansjo), plus localities in Greenland, India, and other Precambrian shields. It is uncommon and largely of scientific/collector interest.
Frequently asked questions
What is eulysite?
Eulysite is a rare iron-rich metamorphic rock built around fayalite (iron olivine) with iron-rich pyroxene, amphibole, and almandine garnet. It forms by high-grade metamorphism of iron-rich, often manganese-bearing sediments.
How can you tell eulysite from eclogite?
Eclogite combines red garnet with green sodic pyroxene (omphacite) and is typically very dense. Eulysite is dominated by iron olivine and other iron silicates rather than green omphacite.
Is eulysite magnetic?
Often yes. Eulysite commonly contains magnetite, so a specimen may attract a magnet and feels heavy because of its iron-rich mineralogy.
Where is eulysite found?
It occurs in high-grade granulite-facies terranes, with the classic occurrences in Sweden and additional localities in Greenland, India, and other ancient shield regions.
Eulysite identified by the community
Recent Eulysite specimens identified with Rock Identifier.
