THE MINERAL DRAVITE (Tourmaline)
- Chemistry: NaMg3(Al,Fe)6Si6O18(BO3)3(OH)4, complex Sodium Magnesium Iron Boro-Aluminium Silicate
- Class: Silicates
- Subclass: Cyclosilicates
- Group: Tourmalines
- Uses: mineral collection specimens
Specimens
Dravite is brown, and will sometimes produce rather large well-shaped crystals that are important specimens in a rock hound's collection.
PHYSICAL CHARACTERISTICS:
- Color is light brown to dark brown.
- Crystal Habit is typically elongated three sided prisms. The terminations can be either a simple to complex trigonal pyramid or a flat basal face. The prism faces are striated lengthwise. In cross section, all tourmalines will appear predominantly triangular in shape with some crystals showing a hexagon. Doubly terminated crystals are hemimorphic meaning that the two ends of the crystal are not exactly alike. Massive forms can also be found.
- Transparency: crystals are translucent to opaque.
- Crystal System is Trigonal; 3m
- Hardness is 7 - 7.5
- Specific Gravity is 3.2+ (slightly heavier than average)
- Cleavage is absent although there is basal parting.
- Fracture is uneven to conchoidal.
- Luster is vitreous.
- Associated Minerals include those associated with metamorphic rocks such as micas, feldspars and quartz.
- Other Characteristics: crystals are brittle and refractive indices = 1.62 and 1.68 .
- Notable Occurances include brazil and some other South American countries, and Africa.
- Best Field Indicators are crystal habit, triangular cross-section, color and hardness.
 Amethyst Galleries' Mineral Gallery MINERALS |
DRAVITE specimen dra-1
$ 105.00
$ 105.00
Dims: 2.1" x 2.0" x 1.8"(5.3 x 5.1 x 4.6 cm)
Wt: 7.25 oz.(205.5 g)
Yinnietharra, western Australia
A very impressive piece, this specimen consists of a single crystal of Dravite, a brown variety of tourmaline. Though it shows noticeable damage, it has excellent hexagonal prismatic crystal form, with six thin secondary faces that truncate the prism angles beween each of the main faces. It is double-terminated, and though one of them is quite rough and slightly malformed, both show definite shallow trigonal pyramids. The color is a dark brown, of course, and the crystal has a vitreous luster and is translucent around its edges, and transparent enough to see light reflecting off of internal fractures up to 2 or 3 mm below the surface. These internal fractures pervade the crystal's entire area, and there are a few spots on the surface which show where muscovite has grown into the crystal, disrupting its form where it rests. The few spots of obvious damage are likely due to the crystal's separation from its host. I really think that this specimen is superb because of its form, size, and double-termiantion.
dra-1 ($105.00)
Yinnietharra, western Australia
DRAVITE specimen dra-2
$ 45.00
$ 45.00
Dims: 4.6 x 3.2 x 2.6" (11.7 x 8.1 x 6.6 cm)
Wt: 1 lb., 2.1 oz. (512 g)
Paraiba, Brazil
Two Dravite prisms are partly embedded in the dark mica schist host of this hand specimen. One of these crystals is broken about 1" (2.5 cm) from its base, but the other is complete, in very good condition, and measures 2.9" (7.3 cm) in length and 1.0" (2.5 cm) in diameter. Its trigonal form is very good, with well-defined edges and clean faces that possess a pearly-to-vitreous luster. Close examination of this crystal will reveal that it is in fact 2 crystals that are very heavily intergrown parallel to each other (I will refer to them as a single unit, though) and topped by shallow trigonal domed terminations. It has a black coloration and is essentially opaque.
dra-2 ($ 45.00)
Paraiba, Brazil
DRAVITE specimen dra-3
$ 150.00
$ 150.00
Dims: 3.2 x 2.1 x 1.3" (8.1 x 5.3 x 3.3 cm)
Wt: 6.60 oz. (187.4 g)
Yinniethara, Western Australia
At least 9 Dravite crystals are intergrown in a "parallel association" that makes up the bulk of this specimen. These crystals are in excellent condition, showing very little damage, and though they could be construed as one crystal, all show definite, individual terminations. They reach dimensions of 1.3 x 1.3 x 0.9" (3.3 x 3.3 x 2.3 cm) and show excellent trigonal prismatic form with shallow trigonal pyramidal terminations. Their edges are well-defined and their faces are clean, possessing a bright pearly-to-vitreous luster. All have the standard dark brown color of Dravite, and are only dimly translucent around their edges even in bright sunlight. The crystals are only partly embedded in a matrix of crystalline but shapeless muscovite and what appears to be a small amount of white calcite.
dra-3 ($150.00)
Yinniethara, Western Australia
DRAVITE specimen dra-4
$ 48.00
$ 48.00
Dims: 5.6 x 4.1 x 1.0" (14.2 x 10.4 x 2.5 cm)
Wt: 14.1 oz. (379 g)
Sierra Branca, Paraiba, Brazil
A single Dravite crystal rests in the biotite matrix of this specimen. It has dimensions of 1.3 x 0.9 x 0.7" (3.4 x 2.2 x 1.8 cm) and is in moderately good condition, as one end is damaged. The rest of the crystal, however, is intact and in excellent condition. Its brown color is so dark that it appears black and opaque, though some translucence is visible along its edges under bright light. It has a greasy luster. There are some depressions in the mica host where other, smaller Dravites were removed, but no other crystals are visible.
dra-4 ($ 48.00)
Sierra Branca, Paraiba, Brazil
DRAVITE specimen dra-5
$ 25.00
$ 25.00
Dims: 1.3 x 1.2 x 1.1" (3.3 x 3.0 x 2.7 cm)
Wt: 1.2 oz. (34 g) w/ base
Serra Branca, Minas Gerais, Brazil
This large thumbnail specimen consists of a cluster of heavily intergrown Dravite prisms. They are generally in good condition, as some moderate damage is visible, and reach dimensions of 0.7 x 0.6 x 0.5" (1.8 x 1.4 x 1.2 cm). All have excellent trigonal prismatic form with the standard shallow pyramidal termination, and a few show evidence of double-termination. All are basically black in color and have the standard greasy luster. There is no host rock present, and the specimen is hot-glued onto a flat, square acrylic base.
dra-5 ($ 25.00)
Serra Branca, Minas Gerais, Brazil
DRAVITE specimen dra-6
$ 25.00
$ 25.00
Dims:2.8x2.0x1.6" (7.1x5.1x4.1 cm)
Wt: 3.1oz. (87g)
Serra da Escadinha, Coroaci, Minas Gerais, Brazil
This specimen consists of a cluster of intergrown dravite crystals resting on a matrix of limonite/goethite with minor calcite. The largest dravite crystal measures 1.7" (4.3cm) in length. This specimen shows quite a bit of damage to all sides. Several termination faces are visible on this specimen.
dra-6 ($ 25.00)
Serra da Escadinha, Coroaci, Minas Gerais, Brazil
DRAVITE specimen dra-7
$ 45.00
$ 45.00
Dims:2.9x2.2x2.1" (7.4x5.6x5.3 cm)
Wt: 7.5oz. (212g)
Pakistan
This is a cluster of intergrown dravite crystals growing out of a matrix of massive dravite and muscovite. These dravite crystals are a rich brown in color, and reach 1.1" (2.8cm) in length. Two of the smaller crystals appear to be double terminated, although the matrix obscures some of the termination faces. This specimen shows damage on two sides; only a moderate amount of damage is visible on the display face.
dra-7 ($ 45.00)
Pakistan
DRAVITE specimen dra-8$ 250.00
Dims: 5.1x3.2x3.7" (13.0x8.2x9.5cm)
Wt: 4 lbs. (2.15kg)
Yinnietharra, Western Australia, Australia
This huge single crystal of dravite weighs over 2 kilograms (nearly 5 pounds). It has the proper brown color and vitreous luster of dravite, and while this tourmaline is transparent, you can see no further into the interior than a millimeter or two, due to the many internal fractures and inclusions. Taken as a whole, the crystal has very good form, with three-sided pyramidal terminations at both ends, and with 9 faces on the sides (3 major faces with minor faces at each corner). While the dravite is essentially undamaged, it is intergrown with a large amount of mica and quartz (everything white in the photographs), and the faces are all stepped in a complex pattern, yielding many minor crystal faces and intermediate terminations. The mica is all damaged, much of it broken off at the surface of the dravite. This is a great cabinet specimen, due to its size and shape.
dra-8 ($250.00)Yinnietharra, Western Australia, Australia