THE MINERAL UVITE (A Tourmaline)

  • Chemistry: Ca(Mg, Fe)3Al5MgSi6O18(BO3)3(OH)3, Calcium Iron Magnesium Aluminum Boro-silicate Hydroxide.
  • Class: Silicates
  • Subclass: Cyclosilicates
  • Group: Tourmalines
  • Uses: Only as mineral collection specimens
  • Specimens

Uvite was considered to be a very rare member of the Tourmaline Group, but it is now becoming widely available on the mineral markets. Other more common and more well-known tourmalines are schorl (black, opaque and iron rich) and elbaite (various colors, transparent to translucent, used as a gemstone and lithium rich). less common tourmalines are dravite, liddicoatite and buergerite.

Uvite is the magnesium/iron-rich member of the group and has one notable exception to the typical tourmaline generalized formula. The usual 6 aluminums are reduced to 5, with a magnesium inserted into one of the aluminums' positions. Despite having so many coloring ions like iron and magnesium, some specimens of uvite can be colorless. The typical specimens of uvite on the mineral markets tend to be an interesting dark green to almost black in color. Other properties of uvite seem to fall in the norm for a tourmaline, except uvite tends to form stubby crystals rather than the long prismatic crystals of its close cousins. These crystals, though, are well formed and show all the interesting features that make tourmaline crystals so much fun to collect.

Uvite is a noted skarn mineral. The skarn is a term for a rock that is the product of a chemically unusual magma body that has intruded into and recrystallized a "dirty" limestone. The "dirty" limestone is not composed of just calcite, CaCO3, like "clean" limestone but is mixed with silicates and/or phosphates, etc. This mixing of the hot, chemically unusual liquids and volatiles of the magma with the different minerals of the "dirty" limestones produces some interesting and rare minerals after all the recrystallizing is done.

PHYSICAL CHARACTERISTICS:

  • Color is green, colorless, white, light brown or black.
  • Luster is vitreous.
  • Transparency: Crystals are transparent to translucent, some dark black specimens can look opaque.
  • Crystal System is Trigonal; 3 m
  • Crystal Habit is typically three sided stubby almost tabular crystals. 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.
  • Hardness is 7.5
  • Specific Gravity is 3.0+ (average)
  • Cleavage is absent although there is basal parting.
  • Fracture is uneven to conchoidal.
  • Streak is white.
  • Other Characteristics: Strongly pleochroic and piezoelectric.
  • Associated Minerals include apatite, sphene, zircon and quartz.
  • Notable Occurrences is Sri Lanka; Pierrepont, New York, USA and in other Skarn localities.
  • Best Field Indicators are crystal habit, triangular cross-section, locality, environment, color and hardness.
UVITE specimens:
(hover for more info)
UVITE specimen uvi-1
$ 75.00
Dims: 1.5" x 1.0" x 0.8" (3.8 x 2.5 x 2.0 cm)
Wt: 10.0 g
Brumado Mine, Bahia, Brazil
A cluster of heavily intergrown Uvite platelets makes up this Brazilian specimen. The Uvites have a hexagonal tabular form that are terminated on each side by extremely shallow, trigonal domes. All seem to be in excellent condition, as I can detect only a small amount of damage, and even with their intergrowth, they still have excellent, regular form. Their edges and faces are clean, and show off their vitreous luster. All have a dark olive-greem color that is a bit deeper than that of most peridots. The largest crystal in the cluster is heavily intergrown and only partially exposed; it measures almost exactly 0.5" (1.3 cm) in diameter. There is no host rock- the specimen is composed entirely out of Uvite. I have affixed it inside a domed thimble box for display purposes.
no photo
uvi-1 ($ 75.00)
Brumado Mine, Bahia, Brazil
UVITE specimen uvi-2
$ 130.00
Dims: 2.5" x 1.4" x 0.8" (6.4 x 3.6 x 2.0 cm)
Wt: 1.14 oz. (32.4 g)
Brumado Mine, Bahia, Brazil
This specimen consists of a crust made up of scores of heavily-intergrown Uvite crystals. The largest of these crystals has visible dimensions of 0.5 x 0.2" (1.3 x 0.5 cm), and though it is incomplete and has a warped form, it is undamaged. The entire cluster is likewise free from damage, with the exception of some of the crystals on the crust's edge. All have the hexagonal, almost tabular form that is common for crystals from this locality, but these are thicker than most that I have seen. They are double-terminated with the obligatory shallow trigonal domes, and their form is excellent, though their intergrowth has caused some slight warping in some spots. They have a deep olive-green coloration and a bright, vitreous luster, and are transparent and moderately clear, showing many internal fractures. Besides the Uvite, there is only a single, clear, incomplete quartz crystal visible on the crust's underside. Some of the Uvites are so thick that they could, in effect, be considered prismatic.
no photo
uvi-2 ($130.00)
Brumado Mine, Bahia, Brazil
UVITE specimen uvi-3
$ 95.00
Dims: 2.1" x 1.4" x 1.0" (5.3 x 3.6 x 2.5 cm)
Wt: 1.55 oz. (44.1 g)
Lavro de Pedra Preta, Brumado Mine, Bahia, Brazil
This is the first Uvite specimen that I have seen that does not have the hexagonal tabular "nailhead" form! This particular piece consists of at least 15 intergrown hexagonal prismatic Uvites. Although their forms are somewhat warped due to intergrowth, they all have well-defined edges and faces that show a pearly-to-vireous luster. Their color is a deep gray-green and some of the smaller, thinner crystals show translucence, and even partial transparence. The only other material present on the specimen is calcite, in clusters that include scores of tiny, transparent rhombohedral crystals. They do not exceed 2 mm in any dimension.
no photo
uvi-3 ($ 95.00)
Lavro de Pedra Preta, Brumado Mine, Bahia, Brazil
UVITE specimen uvi-4
$ 90.00
Dims: 1.5" x 1.3" x 0.8" (3.8 x 3.36 x 2.0 cm)
Wt: 20.7 g
Brumado Mine, Bahia, Brazil
Another specimen from the prolific Brumado Mine, this piece is almost entirely made up of intergrown hexagonal tabular Uvite crystals. There is considerable damage on the piece in the form of broken and incomplete crystals, but many are intact and in excellent condition. The largest of these crystals has dimensions of 0.4 x 0.4 x 0.2" (1.0 x 1.0 x 0.5 cm) and all have good form, with clean edges and faces that show a bright, vitreous luster. Their color is a deep forest green that is almost olive in coloration, and all are translucent, showing dim transparence near their edges. Other than the Uvites, there are a few tiny, colorless calcite rhombohedrons in some of the piece's crevices.
no photo
uvi-4 ($ 90.00)
Brumado Mine, Bahia, Brazil
UVITE specimen uvi-6
$ 50.00
Dims: 1.0" x 0.9" x 0.8" (2.5 x 2.3 x 2.0 cm)
Wt: 6.5 g
Brumado Mine, Bahia, Brazil
A cluster of hexagonal tabular Uvite crystals makes up the bulk of this thumbnail specimen. They range in diameter from a few millimeters to about 0.4" (1.0 cm) and are in excellent condition, showing only a small amount of damage. Though the largest crystal is rather warped due to intergrowth, all others show good form; they have well-defined edges and smooth faces that reflect light with a bright, vitreous luster. Their color is a deep olive-green and most show noticeable transparence and clarity, though all seem to be slightly included. Attached to the cluster of intergrown Uvites are two rhombohedral calcite crystals (see the close-up image). They also show good form and are somewhat transparent, though numerous veil-like inclusions make them appear a milky-white color.
no photo
uvi-6 ($ 50.00)
Brumado Mine, Bahia, Brazil
UVITE specimen uvi-7
$ 37.50
Dims: 1.8 x 1.3 x 0.8" (4.5 x 3.3 x 2.1 cm)
Wt: 0.7 oz. (20 g)
Brumado Mine, Bahia, Brazil
Five large Uvites and several very small ones are intergrown to form this hand specimen. These crystals are in excellent condition, showing very little damage, and reach dimensions of 1.4 x 0.6 x 0.5" (3.5 x 1.5 x 1.3 cm). All have excellent trigonal form, in the prismatic, almost columnar habit that is common with all tourmalines. Their color is a deep, dull green and their luster is the standard vitreous, and all are only dimly translucent. There is no base or host material present.
no photo
uvi-7 ($ 37.50)
Brumado Mine, Bahia, Brazil
UVITE specimen uvi-5
$ 25.00
Dims: 1.1 x 1.1 x 0.9" (2.7 x 2.7 x 2.3 cm)
Wt: 0.38 oz. (11.0 g)
Brumado Mine, Bahia, Brazil
This specimen consists of a single large uvite crystal and dozens of small ones intergrown with many tiny clear calcite crystals. These crystals are in excellent condition, showing very little damage. The large crystal (over 1 cm wide) has good trigonal form, in the prismatic, almost columnar habit that is common with all tourmalines. Their color is a deep, dull green and their luster is the standard vitreous, and all are only dimly translucent.
no photo
uvi-5 ($ 25.00)
Brumado Mine, Bahia, Brazil

 


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