Monzonite is an intrusive igneous rock characterized by an approximately equal ratio of plagioclase and alkali feldspar. It lacks the significant quartz content of granite and the high mafic mineral content of diorite, giving it a balanced, medium-grey granular appearance. Collectors typically find it in plutonic bodies where it is studied for its chemical composition and igneous petrology.
Is this monzonite?
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 monzonite with a known reference. Monzonite sits at Mohs 6-7, softer than the next harder reference, harder than the previous one.
- 2Read the textureLook at a fresh break with a hand lens. Texture: Phaneritic. Grain size: Coarse-grained.
- 3Pick out the mineralsComposition: Mostly plagioclase and alkali feldspar, under 5 percent quartz, with minor hornblende and biotite. Identify the two or three most abundant grains.
- 4Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 5Match the color rangeCompare against the expected color range: gray, light gray, pinkish gray.
Often confused with
Monzonite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside monzonite
Minerals reported to co-occur with monzonite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Mohs hardness
- 6-7
- Density
- 2.6-2.9 g/cm³
- Colors
- Luster
- Vitreous
- Transparency
- Opaque
- Rarity
- Common
- Uses
- Decorative, Construction, Architectural stone
- Host rock
- plutonic intrusions
- Texture
- Phaneritic
- Grain size
- Coarse-grained
- Composition
- Mostly plagioclase and alkali feldspar, under 5 percent quartz, with minor hornblende and biotite
Where rockhounds find monzonite
1 mapped spotsClassic worldwide localities
- Monzoni Mountains, Italy
- Sierra Nevada, USA
- British Columbia, Canada
- Harz Mountains, Germany
Field-hunting tip
Where it forms: plutonic intrusions. If you start seeing plagioclase, orthoclase, hornblende in float, you are in the right ground. In the U.S., the densest reported localities are in Idaho. Start trip planning there.
Common questions
How do you identify monzonite?+
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Can I find monzonite in the United States?+
What rocks look like monzonite?+
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Find monzonite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
