Wehrlite Identification Guide
A field guide to Wehrlite, an olivine-clinopyroxene ultramafic rock, and how to distinguish it from dunite, harzburgite and websterite.
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What Wehrlite Looks Like
Wehrlite is a peridotite (ultramafic plutonic rock) made of olivine plus clinopyroxene, with little or no orthopyroxene.
- Color: olive-green to dark green, often weathering to reddish or yellow-brown crusts.
- Luster: granular, glassy olivine plus sub-metallic/glassy clinopyroxene.
- Texture: medium- to coarse-grained, sugary granular interlocking crystals; dense and heavy.
- Form: layers and lenses in layered intrusions, cumulates, and mantle/ophiolite rocks; also as xenoliths.
Step-by-Step Field Checklist
- Confirm ultramafic: dark, dense, dominated by olive and dark green minerals, essentially no feldspar.
- Identify olivine: sugary, glassy, olive-green equant grains; brittle, often fractured; weathers brown.
- Identify clinopyroxene: darker green stubby prisms with ~90 degree cleavage.
- Check for absence of orthopyroxene (no bronzy, satiny-cleaved grains), separating wehrlite from lherzolite/harzburgite.
- Note brown weathering rinds typical of olivine-rich rocks.
Key Diagnostic Tests
- Hardness: olivine 6.5-7, clinopyroxene ~5.5-6.5; a knife will not easily scratch fresh grains.
- Cleavage: olivine poor (conchoidal fracture); clinopyroxene two cleavages near 90 degrees.
- Density: high, ~3.2-3.4 g/cm3.
- Magnetism: often weakly magnetic from accessory chromite/magnetite; serpentinized wehrlite can be more magnetic.
- Acid: no reaction when fresh.
Common Look-Alikes (peridotite classification)
Peridotites are classified by olivine plus which pyroxenes are present:
- Dunite: >90% olivine, almost no pyroxene, more uniformly olive-green and sugary.
- Harzburgite: olivine + orthopyroxene (no significant clinopyroxene).
- Lherzolite: olivine + BOTH pyroxenes.
- Wehrlite: olivine + clinopyroxene (no significant orthopyroxene).
- Websterite/pyroxenite: pyroxene-dominated with little olivine, much less olive-green granular olivine than wehrlite.
The key for wehrlite: olivine + clinopyroxene, lacking orthopyroxene.
Where It Is Found
Wehrlite occurs in layered mafic-ultramafic intrusions, alpine/ophiolite peridotites, and as mantle xenoliths, with examples in the Alps, ophiolite belts, and many cratonic mantle suites worldwide.
Frequently asked questions
What is Wehrlite?
Wehrlite is an ultramafic peridotite composed of olivine and clinopyroxene with little or no orthopyroxene.
How is Wehrlite different from lherzolite?
Lherzolite contains both ortho- and clinopyroxene with olivine, while wehrlite contains only clinopyroxene (plus olivine) and essentially lacks orthopyroxene.
Wehrlite vs dunite, how do I tell them apart?
Dunite is over 90% olivine with almost no pyroxene, whereas wehrlite has a substantial amount of dark green clinopyroxene mixed with the olive-green olivine.
How do you identify Wehrlite in the field?
Find a dense, dark olive-green ultramafic rock with sugary olivine grains and stubby ~90 degree cleaving clinopyroxene, brown weathering rinds, and no bronzy orthopyroxene.