Natural Freshwater Pearl | Gemopedia

Natural freshwater pearls occur in freshwater mollusks without the intervention of humans. These pearls are beautiful accidents of nature caused by an irritant that becomes lodged inside the mollusk. The animal naturally coats the irritant with nacre to protect its sensitive internal tissues, creating a pearl. Natural freshwater pearls are rare and are usually found by fishermen harvesting the mollusks.
Colors
White
, Cream
, Golden
, Silver
, Gray
, Brown
, Black

Natural Freshwater Pearl Classification

Common Name

Natural Freshwater Pearl

Species

Pearl

Variety

Natural Freshwater Pearl

Colors

white, cream, golden, silver, gray, brown, black

Alternate Names

Gemstone Groups

Key Separations

refractive index, birefringence blink, specific gravity and magnification. A "tooth test" is commonly used in which a pearl is rubbed against a tooth; if gritty, this is an indication that the surface is nacre, versus plastic and glass imitations that feel smooth. X-rays are the only nondestructive test to confirm natural versus cultured origin.

Comments

Natural Freshwater Pearl Optical Properties

Transparency

Translucent To Opaque

Refractive Index

1.53-1.685

Birefringence

0.155

Optic Character

NA

Optic Sign

NA

Polariscope Reaction

aggregate (AGG)

Fluorescence

SWUV: Variable, Inert to strong light blue, yellow, green or pink
LWUV: Variable, Inert to strong light blue, yellow, green or pink

CCF Reaction

Pleochroism

Dispersion

Comments

Natural Freshwater Pearl Chemistry & Crystallography

Chemical Name

calcium carbonate + conchiolin and water

Chemical Formula

CaCO3

Synthesis

Crystal System

Orthorhombic

Classification

Organic

Nature

Natural

Crystallinity

Aggregate

Comments

Natural Freshwater Pearl Characteristic Physical Properties

Hardness

3.54

Streak

Specific Gravity

2.66-2.78

Toughness

Fair

Inclusions

Natural freshwater pearls will have an iridescent surface. If the pearl is drilled you can inspect the hole to look for lack of bead nucleus.

Luster

Pearly

Stability

Poor

Fracture

Uneven

Cleavage

None

Comments

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