The Mineral COLEMANITE
- Chemistry: CaB3O4(OH)3-H2O, Hydrated Calcium Borate Hydroxide
- Class: Carbonates
- Subclass: Borates
- Uses: an ore of boron and as a source of borax (a cleaning agent and useful industrial chemical)
Specimens
Colemanite is a secondary mineral, meaning that it occurs after the original deposition of other minerals. The mineral borax is directly deposited in arid regions from the evaporation of water in intermittent lakes called playas. The playas form only in rainy seasons due to runoff from nearby mountain ranges. The runoff is rich in the element boron and is highly concentrated by evaporation in the arid climate. Eventually the concentration is so great that crystals of borax and other boron minerals form. Ground water flowing through the borax sediments at the bottom of the playa is believed to react with the borax and form other minerals such as colemanite. Colemanite is found in geodes within the borax sediment; its exact means of formation are still not well understood.
Colemanite forms small but richly faceted crystals. The short prismatic habit is typical and good crystals with complicated faces are sought after by collectors.
PHYSICAL CHARACTERISTICS:
- Color is white to clear.
- Luster is vitreous.
- Transparency crystals are transparent to translucent.
- Crystal System is monoclinic; 2/m
- Crystal Habits are quite variable, but include the short prismatic crystals always with complicated facets. Equant crystals that appear stubby and bead-like are also common. The crystals are sometimes flattened and can appear bladed. The terminations are either blunted or steeply pyramidal. Also massive, lamellar and granular habits are found.
- Cleavage is perfect in one direction and distinct in another.
- Fracture is uneven.
- Hardness is 4.5
- Specific Gravity is approximately 2.4 (somewhat lower than average)
- Streak is white.
- Associated Minerals are calcite, celestite, borax, ulexite, kernite, hydroboracite and other borate minerals.
- Other Characteristics: exfoliates (peels off) upon heating.
- Notable Occurrences include Yermo, Boron, Death Valley and other California localities, USA; Nevada, USA; Chile and Panderma, Turkey.
- Best Field Indicators are crystal habit, associations, locality, density, cleavage and hardness.
 Amethyst Galleries' Mineral Gallery MINERALS |
COLEMANITE specimen col-1$ 65.00
Dims: 2.38" x 2.38" x 1.5"(6.0 x 6.0 x 3.8 cm)
Wt: 5.01 oz.(142.1 g)
1425 5W, Billie Mine, Inyo County, Death Valley, California, U.S.A.
This is the first substantial specimen of Colemanite that I have seen, and it is splendid! Like David's description, it is composed of a cluster of short prismatic crystals with a complex form and many, many crystal faces that are clean and mostly free from damage. There are no striations to speak of and a vitreous luster that adds to the specimen's brilliance and helps to expose each crystal's transparency. Clarity is good throughout each crystal, with some spots showing excellence. There is no host rock attached to the specimen, which has been glued to a square sheet of styrofoam(painted black). This sheet fits nicely into a plastic display box that is only slightly wider and deeper than the specimen itself. Ah yes, and I forgot to mention one thing- when I first opened up the box and was closely examining the specimen(I mean very closely), my nose started to tingle a bit, so I took a good whiff of the piece. It secretes an acrid odor reminiscent of the one that concentrated hydrochloric acid gives off when it is dissolving calcite! Weird!
col-1 ($ 65.00)1425 5W, Billie Mine, Inyo County, Death Valley, California, U.S.A.
COLEMANITE specimen col-2
$ 15.00
$ 15.00
Dims: 3.25" x 2" x 1.5"(8.3 x 5.1 x 3.8 cm)
Wt: 4.50 oz.(127.7 g)
Boron, California, U.S.A.
This specimen poses a mystery to me. Resting on a bed of some massive mineral that I cannot identify are hundreds of clear, sharp bladed crystals of Colemanite. They are colorless and generally measure about 1/2"(1.3 cm) in length. They have exceptional clarity and moderate damage to individual points, which are spearhead-shaped and have slightly curved acute edges. Where visible, they have a vitreous luster and reflect light quite well. I say "where visible" because many of the blades have small, pale yellow globules on them, some to the extent that only the edges of a blade can be seen. I don't know what this material is- it has a dull, waxy luster and seems to lack crystal form. Besides, a 10-power loupe isn't sufficient to see these deposits anyway. I think that the globules might be made of calcite, but I need reassurrance from someone who has seen material from this locality.
col-2 ($ 15.00)
Boron, California, U.S.A.
COLEMANITE specimen col-3$ 300.00
Dims: 3.25" x 2" x 1.5"(8.3 x 5.1 x 3.8 cm)
Wt: 4.50 oz.(127.7 g)
Boron, Kern County, California, U.S.A.
A really beautiful cabinet-sized specimen, this piece consists of a section of a crust from which grow hundreds of monoclinic, bladed Colemanite crystals. These blades are clustered in sprays that reach maximum dimensions of 1.8 x 1.1 x 0.3" (4.6 x 2.8 x 0.8 cm), and are in generally excellent condition, as they show almost no damage beyond that of their edges. The crystals generally have heights and widths similar to the size of their clusters, but are stacked together, with only their terminations showing any real separation. The blades are colorless and have a vitreous luster, and are transparent and clear, though they do show some cloudy inclusions and internal fractures that spoil their clarity when they are stacked together. The section has these clusters on both sides, though they are much larger on one side than on the other. It is a specimen of very good quality and is rather complex and "busy".
col-3 ($300.00)Boron, Kern County, California, U.S.A.
COLEMANITE specimen col-4
$ 135.00
$ 135.00
Dims: 2.5" x 2.4" x 1.9" (6.4 x 6.1 x 4.8 cm)
Wt: 5.33 oz. (151.2 g)
Boron, Kern County, California, U.S.A.
This lovely specimen is consists of a cluster of sharp, triangular Colemanite blades. These bladed crystals are in generally good condition, though several are damaged, and a few severely so. They have maximum dimensions of 1.4 x 1.1 x 0.3" (3.6 x 2.8 x 0.8 cm) and show excellent monoclinic form, with sharp edges and smooth faces that have a bright, pearly-to-vitreous luster. Individual blades are colorless and transparent, though their clarity is often spoiled by their intergrowth. There is no host rock present, and the intergrown bases of the crystals hold them together.
col-4 ($135.00)
Boron, Kern County, California, U.S.A.
COLEMANITE specimen col-5
$ 50.00
$ 50.00
Dims: 2.0" x 1.2" x 1.1" (5.1 x 3.0 x 2.8 cm)
Wt: 1.08 oz. (30.6 g)
Boron, Kern County, California, U.S.A.
This thumbnail specimen consists of several intergrown clusters of Colemanite blades. These blades range in length from 2 mm to nearly 2" (5 cm). Though several show obvious damage, many others are in good condition and show excellent monoclinic form, with sharp edges and striated but clean faces that have a bright, vitreous luster. The blades are colorless and transparent, though inclusions and their intergrowth make it difficult to see through many of them. There is no host rock of any sort on the piece- I think that this was part of a larger cluster or formation that likely broke off during its mining.
col-5 ($ 50.00)
Boron, Kern County, California, U.S.A.
COLEMANITE specimen col-6
$ 30.00
$ 30.00
Dims: 2.4" x 1.7" x 1.6" (6.1 x 4.3 x 4.1 cm)
Wt: 2.17 oz. (61.6 g)
Thompson Mine, Inyo County, California, U.S.A.
At least 15 blocky Colemanite crystals are intergrown to form this specimen. These crystals range in diameter from 2 mm to nearly 1" (2.5 cm), and are generally in excellent condition, as only one or two show any substantial damage. Even though they are somewhat warped due to intergrowth, all have good triclinic prismatic form, with well-defined edges and clean faces that possess a pearly-to-vitreous luster. Their color is a uniformly milky-white, and they are essentially translucent, though most of them show patches of transparence. There is no host rock present.
col-6 ($ 30.00)
Thompson Mine, Inyo County, California, U.S.A.
COLEMANITE specimen col-7
$ 35.00
$ 35.00
Dims: 3.6 x 3.3 x 3.0" (9.1 x 8.4 x 7.6 cm)
Wt: 2 lbs., 4.0 oz. (1.022 kg)
Boron, California, U.S.A.
This large hand specimen consists of one of the largest Colemanite crystals that I have yet seen. It has visible dimensions of 4.5 x 3.5 x 2.9" (11.4 x 8.9 x 7.4 cm) and is incomplete due to its intergrowth with other, broken Colemanite crystals and what may have been a base of trona which is not present on the piece. The crystal shows several areas of human-induced damage, but most of it is not severe. Its chubby, monoclinic prismatic form is reasonably good given its intergrowth, and it has well-defined edges and clean faces that possess a rather dull pearly luster. Its color ranges from colorless to a milky-white, showing respective transparence to translucence. There is only a small amount of what I think is trona that may have been a host rock.
col-7 ($ 35.00)
Boron, California, U.S.A.
COLEMANITE specimen col-8
$ 25.00
$ 25.00
Dims: 3.0 x 2.7 x 1.4" (7.6 x 6.9 x 3.6 cm)
Wt: 5.4 oz. (154.0 g)
near Ryan, Death Valley, Inyo County, California, U.S.A.
This small hand specimen consists mostly of Colemanite by weight; the Colemanite occurs as a crystalline druse that completely envelops a pale brown host rock. The crystals do not exceed 0.1" (3 mm) in any dimension and are generally in excellent condition, as less than 1% of their number show any damage. Though they are heavily intergrown, all have excellent monoclinic prismatic form, with well-defined edges and occasionally striated but clean faces that possess a bright vitreous luster. All are colorless and transparent, though they have a "dirty" discoloration that is likely caused by inclusions of dirt or silt that were trapped during formation.
col-8 ($ 25.00)
near Ryan, Death Valley, Inyo County, California, U.S.A.
COLEMANITE specimen col-9
$ 60.00
$ 60.00
Dims: 3.3 x 2.8 x 1.9" (8.4 x 7.1 x 4.8 cm)
Wt: 8.0 oz. (226.0 g)
Death Valley, Inyo County, California, U.S.A.
Dozens of triangular Colemanite blades are intergrown to make up this hand-sized specimen. According to the included documentation, they are of a form known as shark's teeth, due to their flat, triangular form. The specimen is generally in good condition, though there are several crystals that are obviously damaged and broken. Their form is quite good, with sharp edges and clean faces that possess a dull pearly-to-waxy luster. All are colorless as individuals, but have a generally milky white coloration in their cluster. Each crystal is transparent and dimly to moderately clear, though all contain some cloudy inclusions and are considerably internally fractured; these internal fractures reflect light with an unusually bright luster that makes me think of those found in apophyllite crystals. There is no host rock present- the entire specimen is made up of either crystalline or massive Colemanite.
col-9 ($ 60.00)
Death Valley, Inyo County, California, U.S.A.
COLEMANITE specimen col-10
$ 48.00
$ 48.00
Dims: 1.5 x 1.4 x 1.4" (3.8 x 3.6 x 3.6 cm)
Wt: 26.8 g w/ foam base
1525 level, 5w drift, Billie Mine, Inyo County, California, U.S.A.
A cluster of scores of intergrown Colemanite crystals makes up this thumbnail specimen. They are generally in very good condition, showing sparse to moderate damage, and range in size from a few millimeters along each axis to 0.5 x 0.4 x 0.3" (1.3 x 1.0 x 0.8 cm). Their monoclinic prismatic form is excellent- all have well-defined edges and clean faces that possess a bright, vitreous luster. All are colorless and transparent, though high clarity is usually restricted to the tip of each crystal, with the rest being cloudy and milky-white in color. There is no host rock present.
col-10 ($ 48.00)
1525 level, 5w drift, Billie Mine, Inyo County, California, U.S.A.
COLEMANITE specimen col-11
$ 40.00
$ 40.00
Dims: 4.0 x 2.2 x 2.2" (10.2 x 5.6 x 5.6 cm)
Wt: 11.9 oz. (338.0 g)
White Monster Mine, Inyo County, California, U.S.A.
Hundreds of Colemanite blades coat part of the beige host rock of this hand specimen. However, only a few dozen exceed 0.1" (3 mm) in length, so I will concentrate on them. These larger crystals acheive lengths of up to 0.8" (2.0 cm), and though a few of them are visibly damaged and broken, most are in excellent condition. Their monoclinic bladed form is also very good- all have well-defined edges and clean faces that possess a pearly luster. Their coloration is their most unusual trait, as all are colorless and slightly cloudy at their bases, but clear up and turn a pale brown color towards their terminations (see the second image). The host rock on which they rest is made up mostly of dirty, compact granules of Colemanite, but there seems to be a small amount of clay or siltstone present, too.
col-11 ($ 40.00)
White Monster Mine, Inyo County, California, U.S.A.
COLEMANITE specimen col-12
$ 45.00
$ 45.00
Dims: 1.5 x 1.2 x 1.0" (3.8 x 3.0 x 2.5 cm)
Wt: 23.6 g w/ foam base
1390W level, 4W drift, Billie Mine, Inyo County, California, U.S.A.
At least 12 intergrown Colemanite crystals make up this thumbnail specimen. These crystals are generally in good condition, though a few are damaged and one or two are broken and incomplete. They reach maximum visible dimensions of 0.4 x 0.4 x 0.2" (1.0 x 1.0 x 0.5 cm) and have excellent monoclinic prismatic form that has an almost pseudo-rhombohedral appearance. They have well-defined edges and clean faces with a nearly vitreous luster. All are colorless, transparent, and moderately to dimly clear, depending on the level of internal fracturing present. A small amount of a dull, pale brown host rock is present, and the piece is hot-glued onto a black foam base.
col-12 ($ 45.00)
1390W level, 4W drift, Billie Mine, Inyo County, California, U.S.A.
COLEMANITE specimen col-13
$ 25.00
$ 25.00
Dims:4.1x3.2x3.0" (10.4x8.1x7.6 cm)
Wt: 27.3oz. (774g)
Death Valley, Inyo cty., California
The matrix of this specimen has a large vein of colemanite and celestite running through it. On one side, there is a cavity filled with crystals of these minerals to 0.7" (1.8cm). The matrix of this specimen is composed of many tiny crystals of what appears to be celestite. The matrix fluoresces pale yellow. Several crystals on the edges of the cavity are broken; overall, though, most are intact.
col-13 ($ 25.00)
Death Valley, Inyo cty., California
COLEMANITE specimen col-14
$ 45.00
$ 45.00
Dims:2.7x2.1x1.6" (6.9x5.3x4.1 cm)
Wt: 4.1oz. (116g)w/base
Billie Mine, Inyo cty., California
This specimen consists of a cluster of colemanite crystals dominated by one large colemanite crystal. The large crystal measures 2.1" (5.3cm) in length. All of the crystals are translucent, and milky white in color. The large crystal shows damage on the back side, and the other crystals show minor to moderate damage, as well. This specimen is securely glued to a styrofoam base.
col-14 ($ 45.00)
Billie Mine, Inyo cty., California