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Tourmaline · Variety of Tourmaline

Schorl

Opaque black with characteristic striated prismatic crystals

Black
Optical properties

Optical characteristics

Ref. index
1.635 – 1.675
Birefringence
0.017 – 0.03
Luster
Vitreous to resinous
Pleochroism
Strong Opaque in gem use; very thin sections show dark green to black under transmitted light.
Fluorescence
Inert.
Origins

Source localities

Russia Russia: Ural Mountains / Siberia
Significant

Classic source for alexandrite, demantoid, diamond and nephrite.

20% est. supply
Brazil Brazil: Minas Gerais / Paraíba / Bahia
Commercial

Major source for beryl, tourmaline, quartz, topaz, chrysoberyl and rare minerals.

30% est. supply
United States USA: major gem fields
Commercial

Diverse sources for turquoise, tourmaline, opal, sapphire, topaz, red beryl and rare minerals.

15% est. supply
Namibia Namibia: Erongo / Green Dragon area
Commercial

Known for demantoid, spessartite and collector minerals.

15% est. supply
Worldwide Worldwide
Commercial

Broad worldwide occurrence or distribution.

20% est. supply
Inclusions

Inclusions & features

Needles Growth Tubes, Rain Inclusions Under 10x loupe: long thin hollow channels running parallel to each other and to… Zoning Color Zoning Under 10x loupe in immersion: bands or patches of deeper or lighter color arranged…
Identification

Instruments used

10x Loupe Your most-used instrument, start every examination here Hydrostatic Scale Measures specific gravity, works even on opaque stones Polariscope Determines single vs. double refraction, quick and conclusive