Dravite
Dravite is a member that is rare of Tourmaline Group of minerals that includes Achroite, Dravite, Liddicoatite, Povondraite, Rubellite, Uvite and Schorl. Dravite is a magnesium member that is rich of Tourmaline Group. Other more common and more well know Tourmalines are Elbaite colors that are(various colorless, lithium rich), Schorl (opaque black, iron rich), Uvite and Liddicoatite. Most Tourmaline that is colored used gemstones are Elbaite Tourmaline. Dravite is named for the river Drau (in Latin, Drave), on that the kind locality is found. Its available in colors of brown to black, red, yellow, blue, green, colorless, colorless and white to yellow in thin section.
Distribution: Discovered around Dravograd (Unterdrauberg), Slovenia. From Beura, Val d’Ossola, Piedmont, Italy. At Arendal and Snarum, Norway. From Outokumpu, and Kaavi, Kuopio, Finland. In the USA, ¯ne crystals from Gouverneur, Pierrepont, and Macomb, St. Lawrence Co., New York; at Franklin and Hamburg, Sussex Co., New Jersey; and Newry, Oxford Co., Maine. In Canada, in Hull Township, Quebec; at Wilberforce, Ontario; and a number of other places. From Brumado, Bahia, Brazil. Large crystals from Yinnietharra, 800 km north of Perth, Western Australia. At Osarara, Narok district, Kenya. From Gujarkot, Nepal. Increasingly distinguished from other tourmaline group members.
| Chemical Formula: | NaMg3Al6(BO3)3Si6O18(OH)4 |
| complex Sodium Magnesium Boro-Aluminum Silicate Hydroxide | |
| Molecular Weight: | 958.75 gm |
| Composition: | Sodium | 2.40 % | Na | 3.23 % | Na2O |
| Magnesium | 7.61 % | Mg | 12.61 % | MgO | |
| Aluminum | 16.89 % | Al | 31.90 % | Al2O3 | |
| Silicon | 17.58 % | Si | 37.60 % | SiO2 | |
| Boron | 3.38 % | B | 10.89 % | B2O3 | |
| Hydrogen | 0.42 % | H | 3.76 % | H2O | |
| Oxygen | 51.73 % | O | |||
| 100.00 % | 100.00 % | = TOTAL OXIDE |
| Crystallography: | Trigonal – Ditrigonal Pyramidal |
| Crystal Habit: | Crystals equant or short to long prismatic, with dominant pyramid faces, to 20 cm. Striated || [0001], cross sections typically triangular with curved convex sides. Commonly radiating, granular, and massive. |
| Tw
inning: |
Rare, on {1011} and {4041) |
| Cleavage: | Very poor on {1120},{1011} |
| Fracture: | Irregular/Uneven, Conchoidal |
| Tenacity: | Brittle |
| Moh’s Hardness: | 7.0 |
| Density: | 3.03 – 3.18 (g/cm3) |
| Luminescence: | Fluorescent; yellow to orange under SW UV. |
| Radioactivity: | Not Radioactive |
| Color: | Brown to black, red, yellow, blue, green, colorless, white; colorless to yellow in thin section |
| Transparency: | Transparent to Translucent |
| Luster: | Vitreous to Resinous |
| Refractive Index: | 1.612 – 1.661 Uniaxial ( – ) |
| Birefringence: | 0.0190 – 0.0250 |
| Dispersion: | 0.017 |
| Pleochroism: | Very strong; O = pale yellow; E = colorless, yellowish, greenish, brownish |
