Tourmaline is the birthstone of October. It shares this distinction with Opal.
(Na,Ca)(Mg,Li,Al,Fe2+)3Al6(BO3)3Si6O18(OH)4 – Elbaite, Schorl, and Dravite
(Na,Ca)(Mg,Li,Al,Fe2+,Fe3+)3(Al,Mg)6(BO3)3Si6O18(OH,O,F)4 – Uvite, Liddicoatite, and Buergerite
Specific Gravity: 2.9- 3.3
Hardness: 7.0- 7.5
Crystal System: Hexagonal
Color: Varied in color which include black, brown, green, red, pink, blue, gray, white, colorless, yellow, orange and purple. Crystals are frequently multicolored with two or more distinct colors.
Fracture: Conchoidal to uneven
Rock Type: Igneous, Metamorphic
Achroite- Colorless variety of Elbaite Tourmaline
Buergerite- Rare member of the Toumaline group, occurring almost exclusively at Mexiquitic, San Luis Potosi, Mexico.
Dravite- Member of the Tourmaline group, usually brown in color, the term may be a corrupted to include all forms of brown Tourmaline.
Elbaite- Best known member of the Tourmaline group. It is the most transparent and colorful form of Tourmaline. The term Elbaite may be corrupted by the gemstone industry to refer specifically to green Tourmaline.
Indicolite- A blue variety of Elbaite Tourmaline.
Liddicoatite- An uncommon member of the Tourmaline group found primarily Madagascar. It is the calcium analogue of Elbaite, containing calcium in its chemical formula instead of sodium.
Rubellite- Pink to red variety Elbaite Tourmaline.
Schorl- Member of the Tourmaline family. It is black in color and the term may be corrupted to include any very dark Tourmaline forms.
Uvite- An uncommon form of Tourmaline found in metamorphic marbles.
Watermelon Tourmaline- Variety of Elbaite Tourmaline that is green on the outside and red on the inside.
Tourmaline is used in jewelry. Due to the piezoelectric nature of Tourmaline makes it useful as part of high pressure gauges.
Watermelon tourmaline cross sections.
Various colors and hues of tourmaline.
Exemplars of tricolor stones from Brazil.