How to identify Pearl

To correctly identify Pearl (Biogenic calcium carbonate (aragonite/calcite)), check each of these features in order. Many rocks and minerals look alike, so cross-reference multiple properties before deciding.

Step-by-step identification

1. 1

   Color

   Overall color and any zoning or banding

   White, cream, pink, silver, gold, green, blue, black, often with iridescent overtones (orient).

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Pearly (nacreous) to dull, depending on quality and surface condition.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Smooth, often with a slightly gritty feel if rubbed against teeth (a traditional, though not recommended, test for authenticity).

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Microcrystalline aggregates of aragonite platelets, typically hexagonal, arranged in concentric layers.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None, due to its aggregate nature.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Marine and freshwater environments where mollusks thrive, typically in shallow, warm waters for marine pearls, or various freshwater bodies for freshwater pearls. Found within the soft tissues of bivalve and gastropod mollusks.

Key Facts

Hardness

2.5-4.5 on the Mohs scale (variable due to organic content and aragonite/calcite ratio)

Specific Gravity

2.60-2.85 (variable, typically 2.70-2.78 for marine pearls, 2.60-2.70 for freshwater pearls)

Crystal System

Orthorhombic (aragonite) or Trigonal (calcite) - microcrystalline aggregates

Color

White, cream, pink, silver, gold, green, blue, black, often with iridescent overtones (orient)

Luster

Pearly (nacreous)

Transparency

Opaque to translucent

Fracture

Uneven to conchoidal

Cleavage

None

Composition

Calcium carbonate (CaCO3) in the form of aragonite and/or calcite, with an organic binder called conchiolin (approximately 82-92% CaCO3, 4-14% conchiolin, 2-4% water)

Physical characteristics

• Crystal Habit: Concentric layers of microscopic aragonite platelets (typically hexagonal) interlayered with conchiolin.
• Cleavage Type: None
• Fracture Type: Uneven to conchoidal
• Tenacity: Brittle
• Luster Type: Pearly (nacreous)

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