Schorl | Gemopedia

Schorl is the most common species of tourmaline, however, it is not as commonly faceted as its brightly colored brothers and sisters because of its black color. Well-formed schorl crystals make striking mineral specimens and long, thin schorl crystals are frequently found in quartz, called "tourmalinated quartz."
Colors
Very Dark Brown, Very Dark Green, Blueish Black To Black

Schorl Classification

Common Name

Schorl

Species

Tourmaline

Variety

Schorl

Colors

Very Dark Brown, Very Dark Green, Blueish Black To Black

Alternate Names

Gemstone Groups

Key Separations

appearance, refractive index and high birefringence; then optic figure, pleochroism and specific gravity

Comments

Crystal habit is prismatic and may be 3, 6 or 9-sided; often a triangular prism with convex faces, and often long and heavily striated parallel to the c axis. Pyramidal terminations are common. Tourmaline is part of an isomorphous series.Most common form of tourmaline.Dark material might have a birefringence as high as 0.040.Pyroelectric: development of opposite charges at the ends of a tourmaline crystal due to change in temperature. Piezoelectric: development of opposite charges at the ends of a tourmaline crystal when placed under stress.

Schorl Optical Properties

Transparency

Semitranslucent - Opaque

Refractive Index

1.635-1.672

Birefringence

0.018-0.025

Optic Character

Uniaxial

Optic Sign

Negative

Polariscope Reaction

Doubly Refractive (DR)

Fluorescence

SWUV: Variable
LWUV: Variable

CCF Reaction

Pleochroism

Unobservable

Dispersion

Strength: moderate fire Value: 0.017

Comments

Schorl Chemistry & Crystallography

Chemical Name

complex boro-silicate of Al, Mg and Fe

Chemical Formula

Na(Fe2+3)Al6(Si6O18)(BO3)3(OH)3(OH)

Synthesis

Crystal System

Trigonal

Classification

Silicate

Nature

Natural

Crystallinity

Crystalline

Comments

Schorl Characteristic Physical Properties

Hardness

7-7.5

Streak

White

Specific Gravity

3-3.26 Range:0.2/-0.06 Typical:3.06

Toughness

Good

Inclusions

Schorl often has tube-like 2-phase inclusions running parallel to crystal's principle axis, film-like, irregular or thread-like liquid inclusions, angular thin film mirror-like inclusions, gas inclusions in mesh-like pattern, parallel oriented hollow tubes or needles.

Luster

Vitreous

Stability

Very Good

Fracture

Conchoidal, Uneven

Cleavage

Poor, in two directions

Comments

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