Tourmaline | Gemopedia

Once proposed to be the national gemstone of the United States, tourmaline is found all over the world and in a variety of colors. Tourmaline is the most colorful of all gemstones because, according to an ancient Egyptian legend, it passed through a rainbow on its journey to Earth and brought all of the colors of the rainbow with it. Tourmaline is a mineral group comprised of multiple species of complex borosilicates. Lovingly referred to by mineralogists as the garbage can mineral, its crystal structure allows for the incorporation of a wide range of elements, many of which cause the stunning color varieties and spectacular zoning of tourmaline, including copper, manganese, iron, and titanium. Major tourmaline species include liddicoatite, dravite, uvite, schorl, and elbaite.
Alternate Names
Achroite, Bi-Color Or Parti-Colored, Chrome Tourmaline, Dravite, Elbaite, Fluor-Buergerite, Indicolite, Liddicoatite, Povondtaite, ParaBa Tourmaline, Rubellite, Schorl, Uvite, Verdelite, Watermelon
Colors
Light To Strong Pink, Orangy Red, Red, Purplish Red, Purple, Inky Blue, Blue, Bluish Violet, Violet, Greenish Blue, Light To Dark Green-Blue To Yellowish Green, Dark Green, Yellow, Orange, Brown, Dark Brown, Black, Rarely Colorless

Tourmaline Classification

Common Name

Tourmaline

Species

Elbaite, Dravite, Schorl

Variety

Colors

Light To Strong Pink, Orangy Red, Red, Purplish Red, Purple, Inky Blue, Blue, Bluish Violet, Violet, Greenish Blue, Light To Dark Green-Blue To Yellowish Green, Dark Green, Yellow, Orange, Brown, Dark Brown, Black, Rarely Colorless

Alternate Names

Achroite, Bi-Color Or Parti-Colored, Chrome Tourmaline, Dravite, Elbaite, Fluor-Buergerite, Indicolite, Liddicoatite, Povondtaite, ParaBa Tourmaline, Rubellite, Schorl, Uvite, Verdelite, Watermelon

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. Misnomers: Brazilian sapphire-blue tourmaline; Brazilian emerald, Ceylonese peridot-green tourmaline. Achroite: colorlessBi-color or parti-colored: tourmaline with two colors and multiple colors. Chrome tourmaline: fine intense green usually colored by chrome or vanadium. Dravite: yellow or brown tourmaline. Elbaite: a sodium lithium aluminum tourmaline species. Fluor-buergerite: bronzish-brown to dark-brown to almost black with bronze schiller. Indicolite or indigolite: violetish blue to greenish blue. Liddicoatite: a calcium lithium tourmaline species. Povondtaite: dark brown, brownish black to black with resinous luster. Paraba tourmaline: a neon blue to green colored cuprian Elbaite tourmaline originally found in the Brazilian State of Paraiba. Rubellite: deep pink to red stones. Schorl: black, brownish black or blueish black stones. Uvite: a calcium magnesium aluminum tourmaline species. Verdelite: dark green,yellowish green, brownish green to blueish green. Watermelon: pink center with green edges. Birefringence is typically around 0.020 but dark material can be up to 0.040 October birthstone. 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.

Tourmaline Optical Properties

Transparency

Transparent - Opaque

Refractive Index

1.624-1.644
Tolerance:-1.22222222222222

Birefringence

0.018-0.04

Optic Character

Uniaxial

Optic Sign

Negative

Polariscope Reaction

Doubly Refractive (DR)

Fluorescence

SWUV: Inert to weak red to violet
LWUV: Inert to weak red to violet

CCF Reaction

Pleochroism

Dichroic, moderate to strong, varying shades of body color

Dispersion

Strength: weak fire Value: 0.017

Comments

Tourmaline Chemistry & Crystallography

Chemical Name

complex boro-silicate of Al, Mg and Fe

Chemical Formula

(Ca,K,Na)(Al,Fe,Li,Mg,Mn)3(Al,Cr,Fe,V)6(BO3)Si6O18(OH,F)4

Synthesis

Crystal System

Trigonal

Classification

Silicate

Nature

Natural

Crystallinity

Crystalline

Comments

Tourmaline Characteristic Physical Properties

Hardness

7-7.5

Streak

White

Specific Gravity

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

Toughness

Fair

Inclusions

Green tourmaline is a type I clarity stone. Blue, purple, red, orange, yellow and bi-color or parti-colored tourmaline is a type II clarity stone. Red and watermelon tourmaline are type III clarity stones. Tourmaline might contain tube-like 2-phase inclusions running parallel to crystal's principle axis, film-like, irregular or long and thin liquid inclusions, angular thin reflective inclusions, gas inclusions in net-like pattern, parallel oriented hollow tubes, needles.

Luster

Vitreous

Stability

Very Good

Fracture

Conchoidal

Cleavage

Poor, in two directions

Comments

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