Iceland Spar | Gemopedia

The colorless, transparent variety of calcite is called "Iceland spar," an important variety for its use in optics, including gemological dichroscopes. Originally discovered in Iceland, gems are most often sold as cleavage pieces that beautifully demonstrate calcite's unique birefringence, or double refraction. Because it is a natural polarizing filter, many believe it was used as a navigational tool by ancient Vikings.
Alternate
Names
Icelandic Spar
Colors
Colorless, Possible Very Pale Yellow

Iceland Spar Classification

Common Name

Iceland Spar

Species

Calcite

Variety

Iceland Spar

Colors

Colorless, Possible Very Pale Yellow

Alternate Names

Icelandic Spar

Gemstone Groups

Calcite

Key Separations

cleavage, refractive index, birefringence, strong doubling (if transparent), specific gravity. Use birefringence blink method.

Comments

When colorless and transparent, the variety is called "Iceland spar," an important variety for its use in dichroscopes. Most often sold as cleavage pieces.

Iceland Spar Optical Properties

Transparency

Transparent

Refractive Index

1.486-1.658

Birefringence

0.172-0.172

Optic Character

Uniaxial

Optic Sign

Negative

Polariscope Reaction

Doubly Refractive (DR)

Fluorescence

SWUV: Variable
LWUV: Variable

CCF Reaction

Pleochroism

None

Dispersion

Strength: moderate fire Value: 0.017

Comments

Iceland Spar Chemistry & Crystallography

Chemical Name

calcium carbonate

Chemical Formula

CaCO3

Synthesis

Crystal System

Trigonal

Classification

Carbonate

Nature

Natural

Crystallinity

Crystalline

Comments

Iceland Spar Characteristic Physical Properties

Hardness

3

Streak

Specific Gravity

2.65-2.75 Range:+/-0.05 Typical:2.7

Toughness

Poor

Inclusions

Iceland spar is identified by strong eye visible doubling and might show adularescence.

Luster

Vitreous

Stability

Fair

Fracture

Uneven, Granular, Splintery

Cleavage

Perfect, in three directions

Comments

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