Coral (Calcareous) | Gemopedia

Coral has been prized throughout history for its natural beauty. Like pearl, coral is also an organic gem consisting of more than 90% calcium carbonate. All coral consists of the remains of skeleton-like support structures that were built by colonies of very small marine animals, known as coral polyps. Proteinaceous coral differs from calcareous coral because it is made up of strong keratin proteins.
Colors
Light Pink, Dark Red, Orange, White, Cream, Blue, Purple

Coral (Calcareous) Classification

Common Name

Coral (Calcareous)

Species

NA

Variety

Colors

Light Pink, Dark Red, Orange, White, Cream, Blue, Purple

Alternate Names

Gemstone Groups

Key Separations

RI, birefringence blink, magnification and fluorescence

Comments

Misnomer: polypite

Coral (Calcareous) Optical Properties

Transparency

Semitranslucent - Opaque

Refractive Index

1.486-1.658

Birefringence

0.172-0.172

Optic Character

Optic Sign

Polariscope Reaction

Aggregate (AGG)

Fluorescence

SWUV: White:inert to weak to strong bluish whiteLight and dark orange, red and pink: inert to orange to pinkish orangeDark red: inert to dull red to purplish red
LWUV: White:inert to weak to strong bluish whiteLight and dark orange, red and pink: inert to orange to pinkish orangeDark red: inert to dull red to purplish red

CCF Reaction

Pleochroism

None

Dispersion

Comments

Coral (Calcareous) Chemistry & Crystallography

Chemical Name

calcium carbonate

Chemical Formula

CaCO3

Synthesis

Crystal System

NA

Classification

Organic

Nature

Natural

Crystallinity

Non-Crystalline

Comments

Coral (Calcareous) Characteristic Physical Properties

Hardness

3.5-4

Streak

Specific Gravity

2.6-2.7 Typical:2.65

Toughness

Fair

Inclusions

Calcareous coral has a wavy fibrous structure with polyp cavities in cross section the branches have concentric web like structure.

Luster

Vitreous

Stability

Poor

Fracture

Uneven, Splintery

Cleavage

None

Comments

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