Amphibolite is a metamorphic rock composed mainly of amphibole minerals like hornblende and plagioclase feldspar. It is characterized by its dark, often foliated or banded appearance and typically forms through the regional metamorphism of mafic igneous rocks.
Is this amphibolite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch amphibolite with a known reference. Amphibolite sits at Mohs 5-6, softer than the next harder reference, harder than the previous one.
- 2Read the textureLook at a fresh break with a hand lens. Texture: Weakly foliated or schistose.
- 3Pick out the mineralsComposition: Amphibole, especially hornblende and actinolite, with plagioclase and little or no quartz. Identify the two or three most abundant grains.
- 4Read the lusterHold the specimen under a strong light. Luster: subvitreous to pearly.
- 5Match the color rangeCompare against the expected color range: black, dark green, dark gray.
Often confused with
Amphibolite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads subvitreous to pearly on Amphibolite and vitreous on Hornblende.
How to tell apart: Luster reads subvitreous to pearly on Amphibolite and pearly on Schist.
How to tell apart: Luster reads subvitreous to pearly on Amphibolite and vitreous on Gneiss.
Often found alongside amphibolite
Minerals reported to co-occur with amphibolite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Mohs hardness
- 5-6
- Density
- 2.9-3.2 g/cm³
- Colors
- Luster
- Subvitreous to pearly
- Transparency
- Opaque
- Rarity
- Common
- Uses
- Decorative, Construction, Architectural
- Host rock
- regional metamorphism of basaltic rocks
- Texture
- Weakly foliated or schistose
- Composition
- Amphibole, especially hornblende and actinolite, with plagioclase and little or no quartz
Where rockhounds find amphibolite
4 mapped spotsClassic worldwide localities
- Adirondack Mountains, USA
- Scotland
- Scandinavia
- Alps
- Canada
Field-hunting tip
Where it forms: regional metamorphism of basaltic rocks. If you start seeing hornblende, plagioclase, garnet in float, you are in the right ground. In the U.S., the densest reported localities are in North Carolina, Maryland, South Carolina. Start trip planning there.
Common questions
How do you identify amphibolite?+
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Find amphibolite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
