How to identify Pearl

To correctly identify Pearl (Biogenic calcium carbonate (aragonite or calcite) and conchiolin), 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

   Typically white, cream, pink, silver, gold, green, blue, or black. The color is influenced by the type of mollusk and its environment.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Pearly (nacreous) to silky, often with an iridescent 'orient' due to light interference.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Smooth, often slightly gritty when rubbed gently against a tooth (a traditional, though not recommended, test for authenticity).

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Concentric layers of microscopic aragonite (or calcite) crystals, typically tabular or prismatic, bound by conchiolin.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None, due to its amorphous to cryptocrystalline structure.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Formed within the mantle tissue of marine or freshwater bivalve and gastropod mollusks, typically in shallow coastal waters, lagoons, or freshwater bodies.

Key Facts

Hardness

2.5-4.5 on the Mohs scale (relatively soft)

Specific Gravity

2.60-2.85 (varies slightly with composition and origin)

Crystal System

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

Color

Wide range, including white, cream, pink, silver, gold, green, blue, and black

Luster

Pearly (nacreous) to silky

Transparency

Opaque to translucent

Fracture

Uneven to conchoidal

Cleavage

None

Composition

Calcium carbonate (CaCO3) and conchiolin (organic protein)

Physical characteristics

• Crystal Habit: Concentric layers of microscopic aragonite (or calcite) crystals, often tabular or prismatic, intergrown with conchiolin.
• Cleavage Type: None
• Fracture Type: Uneven to conchoidal
• Tenacity: Brittle
• Luster Type: Pearly (nacreous) to silky

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