Gemological Data:
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Indicolite
Generic Information:
Name Origin: Stone belonging to the Tourmaline Group. It gets its name from “Indigo” which means dark blue.
Main Colors: Intense color from violet-blue to slightly grayish to greenish-blue.
Producing Countries: Indicolite deposits are found in pegmatites and alluvial deposits. The most important supplier is the state of Minas Gerais, Brazil. There are deposits in Namibia, Madagascar, Mozambique, and Nigeria among others.
Common Shapes: As it is a gem that is always intense in color, Indicolite is usually cut in a rectangular, octogonal or antique shape, and always with the sides quite vertical.
Usual Treatment: Heat treatment between 500 to 700°C is used to lighten the original very intense blue a little.
Gemological Data:
| Species: | Blue or indicolite tourmaline |
|---|---|
| Hardness of Mohs: | 7/7,5 |
| Specific Density: | 3,06 (+0,15 / -0,05) |
| Cleavage: | None. |
| Fracture: | Uneven, brittle conical |
| Crystal System: | Hexagonal (trigonal) crystals usually elongated with triangular section and rounded faces, clear striations parallel to the main axis; often, several prisms grow together. |
| Chemical Composition: | (NaLiCa) (Fe₁₁MgMnAl) ₃Al₆ [(OH) ₄ (BO₃) ₃Si₆O₁₈)] Complex aluminum borosilicate of variable composition. |
| Transparency: | Transparent to opaque |
| Refractive Index: | 1,624-1,644 |
| Birefringence: | 0.020 |
| Dispersion: | 0,017 |
| Pleochroism: | Dark-blue and greenish-blue. |
| Luster: | Vitreous |
| Fluorescence: | Weak or none |
