TOURMALINE

     Sometimes pink tourmaline is used as a birthstone for October. It takes its name from the Singhalese word turmamali meaning "mixed precious stones" because they were often confused with other gems.Tourmaline spans the color spectrum from red to violet and in every tone. It also occurs in color combinations in one stone (bi-colored or tri-colored), which accounts for its popularity. The fascinating "watermelon" tourmaline looks just like the inside of a watermelon-red in the center surrounded by a green "rind." 

     Tourmaline is a fairly hard, durable, brilliant, and very wearable stone with a wide choice of colors. It is not as fragile as opal, and is sometimes selected by those who prefer faceted stones. It is a gem of modern times, but nonetheless has found its way to the list of birthstones. Perhaps this honor results from tourmaline's versatility and broad color range. Or perhaps to the fact that red-and-green tourmaline, in which the red and green occur side by side in the same stone, is reminiscent of the turning of October leaves. 

     Tourmalines have an interesting pyroelectricity property -- on gentle heating (100 o C) the crystal develops a positive charge on one end and a negative charge on the other. This charge is strong enough to enable the stone to attract or repel light-weight substances such as ash or dust. Benjamin Franklin used to carry a Tourmaline to demonstrate this magnetic quality. 

TREATMENT: Often heat treated and/or irradiated to improve color. These process are permanent.

MOHS HARDNESS: 7-7.5 (a fairly tough stone suitable for most jewelry)

CHEMICAL COMPOSITION: NaLi 3 Al 6 B 3 Si 6 O 27 (OH) 3 (OH,F)

REFRACTIVE INDEX: o=1.640-1.655 e=1.625-1.650
(The angle light is bent traveling through a gemstone)

DENSITY (SPECIFIC GRAVITY): 3.01-3.06
(The number of times heavier a gemstone is compared to water)

PRINCIPAL SOURCES: Brazil, Africa, USA