Tourmaline
Tourmaline is a large family of minerals composed of a complex boro-silicate. The most common species of the tourmaline group is Elbaite (named after the island of Elba in the Mediterranean) and it occurs in all colors of the rainbow. It was first brought to Europe by Dutch traders whom also discovered its pyro-electric effect. When heated, tourmaline is electrically charged, this charge was used to attract ashes from a smoked pipe and these stones thus received the glorious name of asschentrekker (old Dutch for ash puller).
Image courtesy of Lang Antiques
There are many color varieties in the tourmaline group and some have distinctive tradenames:
- Rubellite - pink to red
- Verdelite - green
- Indicolite - blue
- Achroite - colorless
- Dravite - brown
- Schorl - black
- Watermelon - pink core with a green periphery
- parti-colored - several colors in one stone
More recently a variety was discovered in the Paraiba state of Brazil which exhibits neon colors. These are also found in the neighboring state Rio Grande do Norte, as well as in Africa.
| Gemological information for tourmaline | |
|---|---|
| Color | All colors |
| Crystal Structure | Trigonal |
| Family | Tourmaline |
| Refractive Index | 1.624-1.644 |
| Durability | Very durable |
| Hardness | 7 |
| Treatments | Sometimes heat treated |
| Tourmaline care | |
| Ultrasonic cleaning | Not safe |
| Steam cleaning | Usually safe |
| Warm soapy water | Safe |
| Chemical attack | Stable |
| Light sensitivity | Stable |
| Heat sensitivity | May change color |
Online G&G articles on tourmaline
- Spring 1936, A New Alexandrite-like Tourmaline Found, p. 7, 2pp.
- Spring 1950, Tourmaline Cat's-eye Studied, p. 289, 1p.
- Spring 1955, Recent Discovery of Fine Gem Tourmaline in Maine, p. 131, 6pp.
- Winter 1955, Nodular Tourmalines, by Sinkankas, p. 237, 2pp.
- Summer 1958, Historic Himalaya Tourmaline Mine (Calif.) reopened, p. 163, 11pp.
- Fall 1964, "Chameleonite" tourmaline, greenish-brown to brownish-green by day and intense brownish-red to reddish-brown by night, p. 214, 2pp.
- Fall 1965, Intense emerald-green tourmaline, p. 340, 2pp.
- Summer 1966, A fine blue-green tourmaline from Mount Mica, Me., p. 43, 2pp. (See also Fall 1966, p. 70, 2pp.)
- Winter 1967, Chrome tourmaline of Tanzania, p. 242, 3pp.
- Spring 1975, New find of gem tourmaline from Newry Mt., Me., p. 19, 6pp.
- Spring 1975, A rock with green tourmaline and ruby, mixed, p. 27, 1p.
- Fall 1977, A Tourmaline with no dichroism, p. 330, 2pp.
- Winter 1977, Imitation Maine Tourmaline, p. 364, 1p.
- Fall 1980, Aschentrekker - the ash-drawer tourmaline, by Betsy Barker, p. 375, 4pp.
- Winter 1980, Exceptional 11 carat tri-color tourmaline, pink, colorless and greenish-blue, p. 400, 2pp.