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.

Hardness

Mohs

Luster

Vitreous; pearly on cleavages and {0001}

Streak

White

Transparency

Transparent to opaque

mineralcommon

Calcite

Also: Iceland Spar, Dogtooth Spar, Nailhead Spar

Hardness: 3
Luster: Vitreous; pearly on cleavages and {0001}
Streak: White
Transparency: Transparent to opaque

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.

mineral

Quartz

Mohs 7

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.

Compare →

Side by side:Calcite vs Quartz

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: 2.7102 g/cm³
Colors: White Colorless Yellow Orange Blue Green Brown Pink Red
Streak: White
Luster: Vitreous; pearly on cleavages and {0001}
Transparency: Transparent to opaque
Crystal system: Trigonal
Crystal habit: Rhombohedral, prismatic, scalenohedral, massive, stalactitic
Cleavage: {1011}, perfect
Fluorescence: Yellow under SW and LW UV
Rarity: Common
Uses: Collector, Decorative, Industrial, Optical
Host rock: A major rock-forming mineral; in limestones, marbles, chalks, a common cement in clastic sedimentary rocks, and as gangue in hydrothermal veins; in alkalic to mafic igneous rocks; common as speleothems in caves

Where rockhounds find calcite

231 mapped spots

Classic worldwide localities

Rossie and Balmat, St. Lawrence Co., New York, USA
Hancock, Houghton Co., and in the Phoenix mine, Keeweenaw Co., Michigan, USA
Galena, Cherokee Co., Kansas, USA
Picher, Ottawa Co., Oklahoma, in the Tri-State district, USA
Helgustadanáma mine, Reydarfjord, Iceland
Alston Moor, Egremont, and Frizington, Cumbria, England

U.S. states with calcite

Each link opens a state-specific list of mapped rockhounding spots that produce calcite.

Field-hunting tip

Where it forms: A major rock-forming mineral; in limestones, marbles, chalks, a common cement in clastic sedimentary rocks, and as gangue in hydrothermal veins; in alkalic to mafic igneous rocks; common as speleothems in caves. If you start seeing dolomite, celestine, fluorite in float, you are in the right ground. Typical habit: rhombohedral, prismatic, scalenohedral, massive, stalactitic. 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.

Browse 231 U.S. spots for calcite →

More calcite photos

$Iceland spar calcite cleavage rhomb showing double refraction$

Common questions

How do you identify calcite?+

Mohs hardness is 3. Luster: vitreous; pearly on cleavages and {0001}. The streak is white. Common colors include white, colorless, yellow, orange.

Where is calcite found?+

Notable localities include Rossie and Balmat, St. Lawrence Co., New York, USA; Hancock, Houghton Co., and in the Phoenix mine, Keeweenaw Co., Michigan, USA; Galena, Cherokee Co., Kansas, USA; Picher, Ottawa Co., Oklahoma, in the Tri-State district, USA; Helgustadanáma mine, Reydarfjord, Iceland.

Can I find calcite in the United States?+

RockHoundR maps 231 calcite rockhounding spots across 12 U.S. states. The top states are Missouri, Utah, New Jersey.

What rocks look like calcite?+

Calcite is most often confused with Quartz, Dolomite, Barite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with calcite?+

Calcite commonly co-occurs with Dolomite, Celestine, Fluorite, Barite, Pyrite, Marcasite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does calcite form in?+

What is calcite used for?+

Calcite is used in collector, decorative, industrial, optical.

Find calcite on the map

RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.