Schorl Tourmaline

SCHORL TOURMALINE

Tourmaline is the name given to a group of related minerals all having essentially the same crystal structure but varying considerably in chemical composition and in some of their physical properties. It is best described as a very complex aluminum borosilicate. There are eleven distinct mineral species of tourmaline based on chemical composition: buergerite, chromdravite, dravite, elbaite, feruvite, foitite, liddicoatite, olenite, povondraite, schorl and uvite.

Tourmaline occurs in all colors. Commonly used names have been given to tourmalines of specific colors or color combinations such as Rubellite for pink to red shades, indicolite for blue tourmaline and watermelon for tourmalines showing concentric color zoning with pink-red cores surrounded by green. Since some species of tourmaline such as elbaite and liddicoatite can look exactly the same and laboratory analysis is necessary to determine the precise tourmaline species, the generally preferred nomenclature today for tourmalines that have not been lab analysed is simply to use the color of the specimen as a prefix followed by tourmaline as in green tourmaline.

The color in tourmaline is due to the presence of metal ions (Fe, Mn, Cr, V, Ti and Cu) in its crystal structure. The color we see in tourmalines is produced when light is absorbed by these ions or by interactions between these ions (intervalent charge transfers).

Some tourmalines form with inclusions of thread-like tubes or cavities which usually occur parallel to the length of the crystal. If these inclusions occur in sufficient number, they may produce a chatoyant effect that yields a cat's-eye when cut into a cabochon gem.

PHYSICAL PROPERTIES

GHEMICAL COMPOSITION

Quartz Na(Fe,Mn)3Al6B3Si6O27(OH)3(OH,F)

CLASS

Cyclosilicates

CRYSTAL SYSTEM

Hexagonal-rhombohedral

CRYSTAL HABIT

Commonly forms prismatic crystals with well developed trigonal prism and second-order hexagonal prism faces, can be elongated or flattened, commonly vertically striated. In cross section the prism faces often round into one another giving the appearance of a spherical triangle. Doubly terminated crystals often show different forms at each end of the vertical axis. Also radiating, acicular, columnar, massive

SPECIFIC GRAVITY

22.96 - 3.31 (buergerite 3.31, dravite 3.03-3.15, elbaite 3.03-3.10, liddicoatite 3.02-3.08, schorl 3.10-3.25 and uvite 2.96-3.06)

INDEX OF REFRACTION

1.610-1.735 (buergerite 1.655-1.735, dravite 1.610-1.661, elbaite 1.615-1.655, liddicoatite 1.621-1.637, schorl 1.625-1.675 and uvite 1.612-1.638)

BIFEFRINGE
0.016-0.080 (buergerite 0.080, dravite 0.021-0.026, elbaite 0.016-0.024, liddicoatite 0.016,schorl 0.025-0.035 and uvite 0.017-0.020)

Pleochroism

Strong

HARDNESS

7.0 - 7.5

COLOUR

Black

LUSTER

Vitreous to resinous, can occur with chatoyancy due to tubular cavities parallel to the C axis

Fracture

Conchoidal, brittle

Schorl rough stocks

OUR STOCKS / ORDER SPECIFICATIONS

Smaller Pieces - 5 grams To 10 grams

Larger Pieces - 10 grams TO 50 grams single pieces.

Minimum Order Supply - 50 Kilograms

Maximum Supply Per Order - 10 Tons

PRICE & SHIPPING COSTS (FOB/CIF), SEND US AN EMAIL FOR THE QUOTATION.

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