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Tourmaline · Variety of Tourmaline

Dravite

Honey-brown to dark brownish-green, colored by iron and magnesium

Brown Yellow-Brown
Optical properties

Optical characteristics

Ref. index
1.634 – 1.668
Birefringence
0.017 – 0.03
Luster
Vitreous
Pleochroism
Strong Strong dichroism: yellow-brown to dark brownish-green depending on crystal axis.
Fluorescence
Inert to weak.
Origins

Source localities

Russia Russia: Ural Mountains / Siberia
Significant

Classic source for alexandrite, demantoid, diamond and nephrite.

17% est. supply
Brazil Brazil: Minas Gerais / Paraíba / Bahia
Significant

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

20% est. supply
Australia Australia: Queensland opal fields
Significant

Important boulder opal source; Australia also produces significant dravite.

18% est. supply
Austria Austria: Tyrol / Zillertal
Major ★ Top Source

Known for alpine minerals and gem crystals; Drava region (Austria/Slovenia) is the type locality for dravite.

22% est. supply
Italy Italy: Val Malenco / alpine localities
Significant

Known for demantoid and collector minerals.

13% est. supply
United States USA: major gem fields
Commercial

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

10% est. supply
Treatments

Enhancement & treatment

Heat Heat Treatment, Tourmaline Heat treatment is used to improve tourmaline color and is often stable. Disclosure is…
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… Crystals Crystal Inclusions Under 10x loupe: solid, well-formed mineral crystals trapped inside the host gem. They may… Fractures Fingerprint Inclusions Under 10x loupe: curved or wavy lines of tiny dots forming patterns that look…
Identification

Instruments used

Refractometer Measures refractive index, the backbone of gem identification Dichroscope Reveals pleochroism, instantly eliminates singly-refractive stones 10x Loupe Your most-used instrument, start every examination here Polariscope Determines single vs. double refraction, quick and conclusive Hydrostatic Scale Measures specific gravity, works even on opaque stones