JAMESONITE specimen jam-4
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.