Sphalerite cut gemstones

Sphalerite gem rough

Sphalerite is a zinc sulphide mineral (Zn,Fe)S that is the chief ore of zinc. While common as massive ore and crystals, gem quality rough is extremely rare. Gems that display flashes of light are prized for their exceptional fire, which is the result of the dispersion of white light into the separate spectral colors. Top grade gem sphalerite specimens exhibit a dispersion value of 0.156, which is three and a half times higher than that of diamonds, at 0.044. In measurements of how light passes through sphalerite, it has a refractive index of 2.37, just slightly less than diamond, at 2.42. Sphalerite is a fairly dense stone, with a specific gravity of around 4.0, so even small cut stones will weigh a comparatively high number of carats for their size.

Crocoite specimen found in the 1960s

In October, 2012 the Red Lead Mine in Dundas, Tasmania was reopened for specimen mining by Collector's Edge minerals and mine owner Shane Dohnt. In the first few months of operation, high quality specimens were found, featuring brilliant color, superior luster, and outstanding translucency. The miners have high hopes for finding world-class specimens similar to those recovered long ago, which sported crystals to over 6" in length. Many feel these crocoites are the best in the world for gemminess and quality.

The Capillitas Mine is the believed to be the world's largest mass of rhodochrosite - famous for its unique formation, occurring as stalactites and stalagmites. Rhodochrosite is a manganese carbonate mineral with the chemical composition MnCO3. The mine is located in the Andalgal√° Department, Capillitas Province, in northwestern Argentina.

Mined since Incan times, the polymetallic sulphide veins at the Capillitas Mine were worked in the 17th century for silver, and later for lead and zinc. Today, sulphides extraction is no longer economical, but the mine is still being worked for and lapidary material for specimens and carving, producing 100-200 tons of material a year. The banded rhodochrosite is often sliced and polished into slabs for collectors.

This is a lovely 9.8 ounce, impressively rich (about 70% silver),
thick slice of silver ore which has formed around cobaltite and other
unusual arsenide minerals, with an estimated bullion value of about $275!

We recently had the opportunity to acquire some 70% pure specimens of sliced silver ore and some 100% pure leaf silver which were collected from the old mine dumps at the Silversmith, Castle and other mines near Cobalt, Ontario. Like leaf gold, leaf silver is quite rare and makes an excellent addition to any elements collection, a silver minerals collection, or a precious metals collection. The slabbed silver ore is also impressive and highly collectible, especially since we are able to sell it for no more than the estimated bullion value!

11.8" Bright Yellow Natural SULFUR STALACTITE - Blue Fire Volcano, Java, Indonesia

Molten sulfur burns atop a solid sulfur deposit at Kawah Ijen volcano

Locality Photos by Olivier Grunewalt
Specimen photos by Treasure Mountain Mining

In Tucson this year, I found a vendor who was selling sulfur stalactites, up to 13" long. The stalactites were a bright, butter yellow color, and consisted of multiple "frozen" rivulets of sulfur. They came from the Kawah Ijen volcano on the island of Java in Indonesia. Here, stalactites form naturally when the molten sulfur drips over the edge of a drop off and "freezes" as it flows along the stalactites as thin rivulets of bright yellow solid sulfur.

We are sad to report that the Rogerley Mine is officially closed. Located in the village of Frosterley in County Durham, England, the mine was operated commercially for mineral specimens in the 1970s, and then was run by from 1999 through August, 2016. The mine workings followed an adit extending northward along the Greenbank vein at the High Flats horizon of the Great Limestone. Colorful specimens of green fluorite crystals, some associated with galena, were recovered from discontinuous mineralized flats on both the east and west sides of the vein.