A pearl is an organic gemstone produced by a living mollusk as a defense against an irritant, composed primarily of calcium carbonate in the form of nacre. It is prized for its orient and luster and occurs in both saltwater and freshwater environments. Collectors value symmetry, color, and surface smoothness.

Hardness

2.5-4.5

Mohs

Luster

Pearly

Streak

White

Transparency

Translucent

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Pearl

Also: Pearl shell

Hardness: 2.5-4.5
Luster: Pearly
Streak: White
Transparency: Translucent

Is this pearl?

5-step field check

Run through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.

1
Test the hardness
Try to scratch pearl with a known reference. Pearl sits at Mohs 2.5-4.5, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Pearl leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Pearl typically shows a pearly luster.
4
Match the color range
Compare against the expected color range: white, cream, pink, gold, black, silver.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: concretionary.

All properties

Chemical formula: CaCO₃
Mohs hardness: 2.5-4.5
Density: 2.6-2.8 g/cm³
Colors: White Cream Pink Gold Black Silver
Streak: White
Luster: Pearly
Transparency: Translucent
Crystal system: Orthorhombic
Crystal habit: Concretionary
Cleavage: None
Fluorescence: Often Inert, But Some May Show White or Blue Under UV
Rarity: Common
Uses: Gemstone, Jewelry
Host rock: Organic Biological Environments (mollusks)

Where rockhounds find pearl

5 mapped spots

Classic worldwide localities

Persian Gulf
French Polynesia
Japan
Australia
Philippines

Field-hunting tip

Look in organic biological environments (mollusks) country, the host setting where pearl typically forms. Field specimens usually show a concretionary habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Wisconsin, Iowa, Tennessee. Start trip planning there.

Browse 5 U.S. spots for pearl →

More pearl photos

Common questions

How do you identify pearl?+

Mohs hardness is 2.5-4.5. It typically shows a pearly luster. The streak is white. Common colors include white, cream, pink, gold.

Where is pearl found?+

Notable localities include Persian Gulf; French Polynesia; Japan; Australia; Philippines.

Can I find pearl in the United States?+

RockHoundR maps 5 pearl rockhounding spots across 3 U.S. states. The top states are Wisconsin, Iowa, Tennessee.

What kind of rock does pearl form in?+

Pearl typically forms in organic biological environments (mollusks). Working float back to the host body is the standard way to chase a fresh occurrence.

What is pearl used for?+

Pearl is used in gemstone, jewelry.

Find pearl on the map

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