Calcite is one of the most common minerals on Earth, occurring in a vast array of crystal habits and colors. It is easily identified by its rhombohedral cleavage, its hardness of 3 on the Mohs scale, and its immediate reaction to dilute hydrochloric acid.
Spotting calcite in the field
Field marks- 1
Fizzes vigorously in dilute acid, which is the definitive test
- 2
Three cleavage directions producing leaning rhombs, never right-angle blocks
- 3
Soft at 3, marked easily by a knife or a copper coin
Calcite is the most common mineral in any limestone country and its acid test is the most reliable single field test in mineralogy. A drop of vinegar will usually do it if you have nothing stronger. Its clear rhombic cleavage fragments show strong double refraction, so a line viewed through one appears doubled, which is a memorable demonstration. It takes an enormous range of crystal forms, more than any other mineral, so shape alone will not identify it.
Straight answers
- Is it worth cutting?
- Too soft for wear. Banded ornamental calcite is carved into bowls and bookends and is widely and misleadingly sold as onyx.
- What is it really worth?
- Very low as material, since it is everywhere. Fine crystal specimens, notably from Elmwood in Tennessee, are genuinely collectible.
- Can you legally keep it?
- Ordinary personal-use collecting rules apply. Active quarries are private and usually accessible only through club visits.
Often confused with
Calcite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Hardness and acid. Calcite is 3 and fizzes, quartz is 7 and does not.
How to tell apart: Dolomite fizzes only weakly and usually only when powdered or in warm acid. Calcite fizzes readily in cold dilute acid.
How to tell apart: Barite is strikingly heavy for a pale mineral and does not fizz.
Often found alongside calcite
Minerals reported to co-occur with calcite. 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
- Transparent
- Crystal system
- Trigonal
- Crystal habit
- Rhombohedral, Prismatic, Scalenohedral, Massive, Stalactitic
- Cleavage
- Perfect in 3 Directions
- Fluorescence
- Often Fluorescent White, Yellow, Or Pink Under SW and LW UV
- Rarity
- Common
- Uses
- Collector, Decorative, Industrial, Optical
- Host rock
- Sedimentary Limestones, Hydrothermal Veins, And Metamorphic Marbles
- Typical price
- $2-20 thumbnail, $30-200 display specimen
Where rockhounds find calcite
215 mapped spotsClassic worldwide localities
- Mexico
- USA
- Iceland
- China
- Germany
- Morocco
U.S. states with calcite
Each link opens a state-specific list of mapped rockhounding spots that produce calcite.
- Missouri29 spots
- Utah21 spots
- New Jersey13 spots
- Pennsylvania11 spots
- Tennessee10 spots
- West Virginia10 spots
- North Carolina9 spots
- Wisconsin9 spots
Field-hunting tip
Look in sedimentary limestones, hydrothermal veins, and metamorphic marbles country, the host setting where calcite typically forms. If you start seeing quartz, fluorite, barite in float, you are in the right ground. Field specimens usually show a rhombohedral, prismatic, scalenohedral, massive, stalactitic habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Missouri, Utah, New Jersey. Start trip planning there.
Common questions
How do you identify calcite?+
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Can I find calcite in the United States?+
How much is calcite worth?+
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Find calcite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
