Monticellite is an uncommon calcium-magnesium silicate belonging to the olivine group. It typically occurs as small, pale prismatic crystals or granular aggregates in contact-metamorphosed limestone and is most often identified by its association with skarn minerals.
Is this monticellite?
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 monticellite with a known reference. Monticellite sits at Mohs 5-5.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous, slightly resinous when massive.
- 4Match the color rangeCompare against the expected color range: colorless, greenish gray, gray.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: crystalline, prismatic.
Often confused with
Monticellite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside monticellite
Minerals reported to co-occur with monticellite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaMgSiO₄
- Mohs hardness
- 5-5.5
- Density
- 3.03-3.27 g/cm³
- Streak
- White
- Luster
- Vitreous, slightly resinous when massive
- Transparency
- Transparent to translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Crystalline, prismatic
- Cleavage
- Poor on {010}
- Rarity
- Uncommon
- Uses
- Collector, Scientific research
- Host rock
- Formed during metamorphism of siliceous dolostones; in contact metamorphic deposits between limestones and olivine gabbros; in skarns at granite-dolomitic limestone contacts; rarely in kimberlites
Where rockhounds find monticellite
1 mapped spotsClassic worldwide localities
- Crestmore, Riverside Co., California, USA
- Cascade Mountain, Essex Co., New York, USA
- Magnet Cove, Hot Spring Co., Arkansas, USA
- Monte Somma and Vesuvius, Campania, Italy
- Scawt Hill, near Larne, Co. Antrim, Ireland
- Isle Cadieux and Oka, Quebec, Canada
Field-hunting tip
Where it forms: Formed during metamorphism of siliceous dolostones; in contact metamorphic deposits between limestones and olivine gabbros; in skarns at granite-dolomitic limestone contacts; rarely in kimberlites. If you start seeing gehlenite, spinel, calcite in float, you are in the right ground. Typical habit: crystalline, prismatic. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Arkansas. Start trip planning there.
Common questions
How do you identify monticellite?+
Where is monticellite found?+
Can I find monticellite in the United States?+
What rocks look like monticellite?+
What minerals are found with monticellite?+
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Find monticellite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
