Chiastolite | Gemopedia

Chiastolite is an opaque variety of andalusite that exhibits a unique cross-like pattern, an internal characteristic caused by carbonaceous inclusions. Sometimes called the "cross stone," this formation is seen in cross-sections of the crystal. Slices are often polished as amulets or for collecting, with no two exactly alike.
Alternate
Names
Macle Or Cross Stone
Colors
White, Gray, Reddish, Light Brown With Black Cross-Like Pattern

Chiastolite Classification

Common Name

Chiastolite

Species

Andalusite

Variety

Chiastolite

Colors

White, Gray, Reddish, Light Brown With Black Cross-Like Pattern

Alternate Names

Macle Or Cross Stone

Gemstone Groups

Key Separations

Appearance, RI and SG

Comments

Often cut as a tablet to display cross pattern.

Chiastolite Optical Properties

Transparency

Translucent - Opaque

Refractive Index

1.63-1.64

Birefringence

0.007-0.013

Optic Character

Biaxial

Optic Sign

Negative

Polariscope Reaction

Aggregate (AGG)

Fluorescence

SWUV: Inert
LWUV: Inert

CCF Reaction

Pleochroism

Unobservable

Dispersion

Comments

Chiastolite Chemistry & Crystallography

Chemical Name

aluminum silicate + carbon

Chemical Formula

Al2SiO5 + C

Synthesis

Crystal System

Orthorhombic

Classification

Silicate

Nature

Natural

Crystallinity

Aggregate

Comments

Chiastolite Characteristic Physical Properties

Hardness

5-5.5

Streak

White

Specific Gravity

3.13-3.2 Typical:3.17

Toughness

Inclusions

Luster

Vitreous

Stability

Fracture

Uneven

Cleavage

Good, in one direction, Poor, in one direction

Comments

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