Colemanite | Gemopedia

A major source of boron, colemanite was discovered in 1884 and named for the California mine owner where it was first found, William Tell Coleman. The color of this stone ranges from colorless to white to grey, sometimes yellowish. Specimens are very sensitive to heat. The short, prismatic crystals are often sought after by collectors and colemanite is rarely seen in the form of gemstones as it presents a challenge to lapidaries as crystals are soft, brittle and have perfect cleavage.
Colors
Colorless To Grayish White, Yellow

Colemanite Classification

Common Name

Colemanite

Species

Colemanite

Variety

Colors

Colorless To Grayish White, Yellow

Alternate Names

Gemstone Groups

Key Separations

RI and birefringence

Comments

Colemanite has a high sensitivity to heat.

Colemanite Optical Properties

Transparency

Transparent - Translucent

Refractive Index

1.586-1.615

Birefringence

0.028-0.03

Optic Character

Biaxial

Optic Sign

Positive

Polariscope Reaction

Doubly Refractive (DR)

Fluorescence

SWUV:
LWUV:

CCF Reaction

Pleochroism

None

Dispersion

Strength: weak fire

Comments

Colemanite Chemistry & Crystallography

Chemical Name

hydrated calcium borate

Chemical Formula

Ca2B6O11.5H2O

Synthesis

Crystal System

Monoclinic

Classification

Borate

Nature

Natural

Crystallinity

Crystalline

Comments

Colemanite Characteristic Physical Properties

Hardness

4-4.5

Streak

White

Specific Gravity

2.4-2.42

Toughness

Poor

Inclusions

Luster

Vitreous

Stability

Fracture

Uneven

Cleavage

Perfect, in one direction

Comments

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