JAMESONITE
Specimen jam-1

Dims: 3.13" x 2.5" x 2.25"(8.0 x 6.4 x 5.7 cm)

Wt: 7.68 oz.(217.7 g)

Pachapaqui Mine, Ancash, Peru

Thousands of fine, hairlike Jamesonite crystals form a mat on the surface of this Peruvian specimen. It is difficult to determine how long the crystals are on average, but I believe that some of them approach 1/4"(about 6 mm) in length. They have a medium dark gray coloration and metallic luster. The matting that they form is so thick that one cannot see the host rock under it. Clusters of tiny calcite crystals mixed with the occasional quartz, however, are visible in parts of the matting where they have come through. The calcite is white, and under magnification looks a lot like rock salt, with a pseudocubic habit that has hopper-crystal and stacking tendencies. The specimen should be handled very carefully to prevent damage and also to prevent exposure to the Jamesonite needles(some fell on my pants and they itch like fiberglass!)

Dims: 3.88" x 3" x 2"(9.7 x 7.6 x 5.1 cm)

Wt: 10.27oz.(291.2 g)

Pachapaqui Mine, Ancash, Peru

I think that this particular specimen is extremely attractive. Amidst a profusion of what I believe are crystals of sphalerite with an unusual, rounded formation and both bladed crystals and round nodules of calcite lie several mattings composed of thousands of Jamesonite crystals. Though none of these appear to be thicker than a human hair, they do achieve lengths of up to 1/2"(1.3 cm). They are a medium-dark gray in color and have a definitely metallic luster. Some of these mattings are made up of such fine crystals that individuality cannot be determined under 10x magnification! Several of these extremely dense mattings are present on the specimen, making the piece look as if a spider tried to cocoon the rock with a gray webbing.

Dims: 5.5" x 2.6" x 2.5" (14.0 x 6.6 x 6.4 cm)

Wt: 2 lbs., 6.6 oz. (1.093 kg)

Noche Bueno, Zacatecas, Mexico

This large hand specimen consists of countless Jamesonite needles that rest on a metallic-sulfide-and-quartz base. These crystals do not exceed 0.5" (1.3 cm) in length or 1 mm in thickness, and appear to be in good condition, though it is very difficult to discern a level of damage. All have a dark gray-black color and a dull metallic luster. Quality of form is also very difficult to determine due to their size. They rest on a layer of crystalline pyrite that shows considerable damage and good pyritohedral form- they have a maximum diameter of 0.5 - 0.7" (1.3 - 1.8 cm) and a rather odd, deep orange-golden color and moderately dull metallic luster. This layer, in turn, rests on a base made up of massive quarz and calcite. The opposite side of this base is covered with a layer of multiple metallic sulfides, all of which have crystalline tendencies but no form.

Dims: 4.4 x 4.0 x 2.4" (11.2 x 10.2 x 6.1 cm)

Wt: 2 lbs., 5.2 oz. (1.111 kg)

Noche Bueno, Zacatecas, Mexico

The bulk of this hand specimen consists of a cluster of several different sulfide minerals, including a substantial number of sprays of Jamesonite needles. From those that are visible, one can see that the Jamesonites average approximately 0.3" (8 mm) in length. Most appear to be in very good condition, as they form in the crevices between the other metallic sulfide crystals, and are thus well protected- there are a few very exposed areas, however, that show damage to all the crystals, including Jamesonite sprays. The needles are too thin to effectively study without relatively high magnification, but they appear to have a reasonably good form and possess a moderate to dull metallic luster. Their color seems to range from a dark gray to an almost coppery-gold, and is likely influenced by the surrounding minerals. The other minerals consist mostly of pyrite and small amounts of sphalerite, and possibly some galena. Many of these crystals are noticeably damaged or broken, and some appear to be decomposed, which likely influenced the coloration of the Jamesonite crystals and that of themselves- there are several small areas that show iridescence, in the form of dull colors. A few milky white hexagonal prismatic quartz crystals are also visible among the sulfides, but most of these are also broken. All of these rest on a base that is made up of crushed bits of sulfide minerals that are cemented together with massive calcite.

Dims:4.2x3.2x2.9" (10.7x8.1x7.4 cm)

Wt: 22.6oz. (641g)

Pachapaqui, Peru

Long slender sprays of jamesonite crystals are scattered over a matrix of pyrite and minor quartz in this specimen. These jamesonite crystals reach up to 1.2" (3.0cm) in length. These crystals are much thicker than the average jamesonite specimen. There is no damage to this piece.

Dims: 1.57x1.18x0.87" (4.0x3.0x2.2cm)

Wt: 1.71oz. (48.3g)

Peru

While mostly pyrite by weight, this specimen displays a fair amount of acicular jamesonite crystals. For the most part, they are tarnished an irridescent blue and are very nice looking. With the aid of a loupe, it is apparent that there is more silvery jamesonite surrounding the blue, there is irridescence in nearly every color of the rainbow, and indeed there are many tiny blue jamesonite crystals scattered over the specimen. The pyrite is brassy in color, and is also host to a few white quartz crystals. There is a bit of putty ("mineral tack") that I can't remove from the bottom, and I am sure that there was a great deal more jamesonite present when the specimen was first mined. It is quite brittle, and I am certain that much of it has broken off.

Dims: 3.13x2.30x0.58" (7.94x5.84x1.46cm)

Wt: 4.81oz (136.0g)

Dalnyegorsk, Russia

One side of this specimen is nearly covered with a fine mat of jamesonite crystals. While most of them are small, a few hundred are nearly a centimeter in length, especially in one area where all of the crystals are longer. Adding to the specimen's aesthetic appeal is that all of these crystals are irridescent, and reflect hues of pink, blue, purple, even some greens and yellows. The reverse side of the specimen is covered with small, flat crystals that are very lustrous, and look like galena to me. They are excellent crystals, although small.