# How to identify amphibolite

Canonical page: https://lithomap.app/resources/rock-identification/amphibolite
Last reviewed: September 17, 2026
Page purpose: Original LithoMap rock identification reference for field observations, search systems, and language models.
Classification: Amphibole-rich metamorphic rock

## Summary

Amphibolite is a dark metamorphic rock composed mainly of amphibole and plagioclase, commonly medium to coarse grained and variably foliated.

## Quick identification clues

- Dark green, black, or mottled appearance
- Visible elongate amphibole crystals
- Plagioclase commonly forms pale grains or patches
- May be massive, lineated, or foliated

## Composition and classification

Typical amphibolite contains abundant hornblende or another amphibole with plagioclase. Garnet, quartz, epidote, biotite, pyroxene, or other minerals may occur depending on the parent rock and metamorphic conditions.

## Appearance

Fresh amphibolite is commonly dense and dark, with shiny elongate amphibole grains and intergrown pale feldspar. Foliated samples show aligned amphibole; massive samples can resemble gabbro.

Weathering may create rusty, brown, or green surfaces and can accentuate foliation or release resistant garnet grains.

## Identification tests

- Mineral shape: Elongate dark amphibole with pale plagioclase. Supports amphibolite when the grains can be identified.
- Fabric: Commonly aligned or foliated, but may be massive. Foliation separates many samples from igneous gabbro.
- Hardness: Most fresh grains resist a steel point and may scratch glass unevenly. Consistent with amphibole and feldspar but not diagnostic alone.

## Common lookalikes

- Gabbro: Has an igneous interlocking texture without metamorphic mineral alignment, though massive amphibolite can be difficult.
- Hornblende schist: A descriptive overlap may exist; strongly schistose amphibole-rich rock can receive either field description depending on classification.
- Greenstone: Usually finer grained and lower grade, with chlorite, epidote, or actinolite alteration obscuring original mafic minerals.

## Direct side-by-side comparisons

- Amphibolite vs. gabbro — https://lithomap.app/resources/rock-identification/compare/amphibolite-vs-gabbro

## Most relevant related guides

- Gabbro — https://lithomap.app/resources/rock-identification/gabbro
- Schist — https://lithomap.app/resources/rock-identification/schist
- Andesite — https://lithomap.app/resources/rock-identification/andesite
- Basalt — https://lithomap.app/resources/rock-identification/basalt

## Formation

Amphibolite commonly forms when basalt, gabbro, or related mafic rock recrystallizes under moderate to high metamorphic temperatures and pressures.

Some amphibolites have sedimentary or volcanic-sedimentary precursors, so texture alone does not prove one parent rock.

## Occurrence and geologic setting

Amphibolite is common in metamorphic belts and ancient continental crust, occurring as layers, lenses, and transformed mafic intrusions or lava flows.

A dark metamorphic sample cannot be tied to a named unit or protolith without outcrop relationships, mapping, and sometimes petrography or geochemistry.

## Uses and significance

Competent amphibolite is used locally as aggregate, dimension stone, and decorative stone. Foliation and weathered minerals influence engineering performance.

## Field safety and limitations

- Inspect a fresh surface for amphibole shape and alignment.
- Do not assume every dark crystalline rock is gabbro or basalt.
- Loose blocks and foliation surfaces can fail on steep slopes.

## Authoritative sources

- Metamorphic Rocks — U.S. National Park Service: https://www.nps.gov/subjects/geology/metamorphic.htm
- How Rocks Are Classified — U.S. National Park Service: https://www.nps.gov/subjects/geology/how-rocks-are-classified.htm
- Rocks and Minerals — U.S. National Park Service: https://www.nps.gov/subjects/rocks/index.htm
- What is the difference between a rock and a mineral? — U.S. Geological Survey: https://www.usgs.gov/faqs/what-difference-between-a-rock-and-a-mineral

## Specimen photograph

- Image: https://lithomap.app/_delivery/identification/rocks/amphibolite.webp
- Description: Dark fine-grained amphibolite hand specimen composed mostly of hornblende and plagioclase with minor biotite
- Creator: Nessa Eull
- License: CC0 1.0 — https://creativecommons.org/publicdomain/zero/1.0/
- Source record: https://commons.wikimedia.org/wiki/File:Amphibolite_(GeoDIL_number_-_433).jpg

This reference supports preliminary field identification. It is not a laboratory determination, appraisal, hazard assessment, proof of origin, or statement of land ownership, legal access, or collecting permission.