CASSITERITE
Specimen cas-3

Dims: 1-3/4" x 1-1/4" x 1/2"

Wt: 1.8 oz

Oruro, Bolivia

This little "heavyweight" is composed of pure Cassiterite, in wonderful, twinned prismatic crystal forms. The largest crystal on the specimen is over 1/2" by 1/2", and itself shows two occurrences of twinning! Twinning in the smaller crystals is more difficult to determine. Color is a dark, black-brown, and though the mass is generally opaque, there are a few small points of translucence. There is some minor damage to some of the crystals' edges, but on the whole, they are quite clean, making a beautiful example out of this specimen.

Dims: 1.5" x 1.3" x 0.9"(3.8 x 3.3 x 1.3 cm)

Wt: 1.58 oz.(45.0 g)

Oruro, Bolivia

This lovely thumabnail specimen has a surprise! There are several crystals of Cassiterite on it, ranging in size from 2 mm to 0.3"(8 mm) in length. They are all a deep, deep brown color, have a vitreous to adamantine luster, and show dim translucence that borders on transparent under halogen light. All of these crystals have excellent form and occur as wedge-shaped prismatic crystals. Some have noticeable damage, but most of these are on the edge of the piece. The most attractive aspect of this piece is a cyclic twin, called a trilling that is in excellent condition. It is a bit misshapen but nearly complete, and looks like a 6-sided tabular prism. There are a few tiny quartz crystals among the Cassiterite; all of this rests on a host rock that seems to be made of more massive versions of both of these minerals.

Dims: 3.0" x 1.2" x 1.2"(7.6 x 3.0 x 3.0 cm)

Wt: 3.93 oz.(111.4 g)

Viloco, Bolivia

More than 15 Cassiterite crystals rest on a bed of crystalline quartz on this specimen. These Cassiterites range in size from 3 mm to 0.4"(1.0 cm) in diameter. They all have a uniform dark brown color, adamantine luster, and dull transparence that is heavily thwarted by the crystals' depth of color and internal fracturing. All have excellent crystal form with little damage and clean faces and edges. Twinning is rampant, and almost all show it; two of the larger crystals show misshapen but definite cyclic twinning, creating trillings. The quartz crystals upon which they rest reach over 0.5"(1.3 cm) in length and are generally milky with a pearly luster. Below them is another layer of crushed Cassiterites, which rests on yet another, thinner crust of quartz crystals. The Cassiterite crystals on this specimen are exceedingly well-defined and easy to study. I am impressed with them!

Dims: 2.2 x 1.6 x 1.2" (6.6 x 4.1 x 3.0 cm)

Wt: 4.6 oz. (131.0 g)

Viloco, Bolivia

This small hand specimen consists of a thin crust of a cream-colored host rock that is coated with a thick layer of crystalline Cassiterite. It almost looks as if the crust consists of two layers of crystals, one on top of the other. The Cassiterites achieve maximum dimensions of 0.4 x 0.3 x 0.2" (1.0 x 0.8 x 0.5 cm), and are generally in excellent condition, as only those crystals at the specimen's edges appear to be damaged. Their form is definitely crystalline, but it is difficult to define it as tetragonal; this is due to the intense intergrowth and twinning that these crystals show. However, their edges are very well-defined and their faces are lightly striated but quite clean, possessing an adamantine luster. All of the crystals have a greenish-brown coloration, though the smaller crystals and those in the low layer are much paler. Most are dark enough in color to be essentially opaque, but in bright light even some of the larger, darker crystals show translucence or even dim transparence. The host rock on which they rest is unknown to me. It is not calcareous, so I would think that it is made up either of shale or quartzite.

Dims: 1.9 x 1.6 x 1.1" (4.8 x 4.1 x 2.8 cm)

Wt: 2.7 oz. (76.3 g)

Viloco, Bolivia

A cluster of Cassiterite crystals partly covers the pale brown host rock of this small hand specimen. These crystals are in generally good condition, though several are obviously damaged or broken. They reach dimensions of 0.6 x 0.4 x 0.3" (1.5 x 1.0 x 0.8 cm) and show reasonably good tetragonal form, though individual crystals are nearly impossible to define due to their intense twinning and intergrowth with each other and the quartz crust on which they rest. Each crystal has well-defined edges and clean faces that possess the standard adamantine luster, however. All have a brown color that deepens as the crystal's size increases. Thus, several of the smallest crystals are noticeably transparent, whereas the largest ones are essentially opaque. They rest on a quartz crust out of which extend several hexagonal prismatic crystals, several of which are damaged. This crust in turn coats the host rock, which I cannot identify.

Dims: 3.3 x 2.6 x 1.4" (8.4 x 6.6 x 3.6 cm)

Wt: 6.1 oz. (171.8 g)

Pingwu, Sichuan Province, China

Several black Cassiterite crystals rest on the muscovite base of this hand specimen. Most are intergrown into confusing clusters, but a few are separate and individual. The largest crystal has visible dimensions of 1.0 x 0.6 x 0.5" (2.5 x 1.5 x 1.3 cm), but is very warped, so that I am not really sure that it is even a single crystal! The other intergrown Cassiterites are also like this, though two of the largest show noticeable twinning. They do show definite crystalline faces, however, that are well-defined and possess a bright subadamantine luster. Their color is essentially black, though under a bright halogen light, one might see small glints of brown color near their edges. The base consists of a thick layer of small intergrown muscovite "books" that rest on a mica-schist base; there are a few small goshenite beryl crystals present in one area, but I think that most of these are incomplete.

Dims: 2.9 x 1.8 x 1.3" (7.4 x 4.6 x 3.3 cm)

Wt: 3.2 oz. (90.5 g)

Pingwu, Sichuan Province, China

Two or three partly intergrown Cassiterite crystals rest on the muscovite host rock of this small hand specimen. The largest crystal is at least 3 times as large as the next largest, and has dimensions of 0.6 x 0.5 x 0.4" (1.5 x 1.3 x 1.0 cm). Only the largest crystal shows any visible damage, and it is minor. All have very good tetragonal form, with slightly disjointed but well-defined edges and striated but clean faces that possess a bright, almost adamantine luster. Their color is essentially black, even under a halogen light, and thus they are opaque. The muscovite base consists of a layer of intergrown "books" that rests atop a layer of finely-grained, massive material. Among the muscovite books rest several small, tabular goshenite beryl crystals (see the close-up image, lower right corner)- these are generally in excellent condition and have excellent hexagonal tabular form, with well-defined edges and clean faces that possess the standard vitreous luster. They are colorless, transparent, and very clear.

Dims:3.7x2.7x2.4" (9.4x6.9x6.1 cm)

Wt: 22.0oz. (625g)

Pingwu, Sichuan prov., China

This is an excellent multiple-species specimen. The left side of the specimen is a solid mass of cassiterite crystals. Crystals reach 1.1" (2.8cm) in length. The right side of the specimen is a mass of muscovite crystals. These crystals reach 0.4" (1.0cm) in length. Finally, growing on and amongst the mica crystals are several superb aquamarine crystals to 0.5" (1.3cm). The aquamarine crystals are odd in that the prism faces did not develop. These crystals are a combination of termination faces; they appear similar to a brilliant-cut faceted stone! All of this rests upon a base of muscovite mica. This is an extremely striking specimen.