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Tourmaline · Variety of Tourmaline

Verdelite

Medium to dark green tourmaline; sometimes yellowish-green or olive-green

Green
Optical properties

Optical characteristics

Ref. index
1.62 – 1.64
Birefringence
0.018 – 0.04
Luster
Vitreous
Pleochroism
Strong Strong dichroism: dark green to lighter yellowish-green; orient perpendicular to c-axis for best color.
Fluorescence
Inert (iron suppresses fluorescence).
Origins

Source localities

Tanzania Tanzania: Merelani Hills
Significant

Sole source of tanzanite worldwide; also produces tsavorite, ruby, sapphire and rare collector gems.

15% est. supply
Brazil Brazil: Minas Gerais / Paraíba / Bahia
Significant

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

35% est. supply
Zimbabwe Zimbabwe: Sandawana
Significant

Classic small but fine emerald source; also produces chrome-rich tourmaline.

10% est. supply
Nigeria Nigeria: Oyo / Ogun / Plateau fields
Significant

Important source for tourmaline, sapphire, garnet, beryl and topaz.

20% est. supply
Mozambique Mozambique: Montepuez / Alto Ligonha / Cuamba
Significant

Major modern source for ruby, garnet, tourmaline and Paraíba-type tourmaline.

20% est. supply
Treatments

Enhancement & treatment

Heat Heat Treatment, Tourmaline Heat treatment is used to improve tourmaline color and is often stable. Disclosure is… Color Enhancement Irradiation, Tourmaline Irradiation can alter tourmaline color centers. It may be used alone or followed by…
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… Multiphase Two-Phase Inclusions Under 10x loupe: a transparent irregular cavity containing both a liquid phase and a…
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 Immersion Microscope See every internal detail clearly, the professional standard