A calcite nodule is a rounded, spherical, or irregular accretion of calcite that forms within sedimentary host rock. Collectors prize it for its interesting shape and often spectacular fluorescence under ultraviolet light.
Is this calcite nodule?
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 calcite nodule with a known reference. Calcite Nodule sits at Mohs 3, 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.
- 4Match the color rangeCompare against the expected color range: white, yellow, gray, brown, colorless.
- 5Look at form & habitCrystal system: trigonal. Typical habit: botryoidal, massive, nodular.
Often confused with
Calcite Nodule vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside calcite nodule
Minerals reported to co-occur with calcite nodule. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaCO₃
- Mohs hardness
- 3
- Density
- 2.71 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Trigonal
- Crystal habit
- Botryoidal, massive, nodular
- Cleavage
- Perfect rhombohedral
- Fluorescence
- Often bright pink or red under SW UV
- Rarity
- Common
- Uses
- Collector, Decorative
- Host rock
- sedimentary limestone or shale
Where rockhounds find calcite nodule
1 mapped spotsClassic worldwide localities
- Missouri, USA
- Kansas, USA
- Oklahoma, USA
- Mexico
- Germany
Field-hunting tip
Where it forms: sedimentary limestone or shale. If you start seeing quartz, pyrite, galena in float, you are in the right ground. Typical habit: botryoidal, massive, nodular. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Missouri. Start trip planning there.
More calcite nodule photos
Common questions
How do you identify calcite nodule?+
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What rocks look like calcite nodule?+
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Find calcite nodule on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
