10.10 ct GREENOCKITE – USA

Greenockite

Pushing another border in cutting… it is a constant challenge to find new materials for gemstone cutting, especially minerals which have never been faceted before because of their properties. We have managed to cut stones that dissolve in water, handled radioactive specimens under strict protection, and even faced poisonous materials—and nobody died! But then there are crystals like Greenockite, which are often just too small, with no larger specimens known to exist on this planet. I have always liked these micros, but the question was how to cut them. Our solution was unorthodox: we faceted these microcrystals by leaving them in the matrix, either gently polishing the crystal faces or faceting the tiny crown while keeping the base anchored. It is a beautiful, experimental way to bring out the fire of a mineral that usually hides in a hand lens.

The Heritage & Discovery

Historical Significance: Greenockite is the primary ore of cadmium, but it rarely occurs in large enough quantities to be mined for the metal alone. Instead, it is a mineralogical prize, known for its intense “cadmium yellow” to orange hues. It represents a rare moment in sulfide chemistry where cadmium manages to isolate itself from zinc. For collectors, it is the “holy grail” of yellow sulfides, offering a level of color saturation that is almost unrivaled in the mineral kingdom.

Discovery: The mineral was first identified in 1840 during the construction of a railway tunnel at Bishopton, Scotland. It was named in honor of Lord Greenock (later the 2nd Earl of Cathcart), who was a keen amateur geologist and the first to recognize the unique nature of these tiny, honey-yellow crystals. Since then, it has been a staple of systematic mineralogy, though always elusive in “gem” sizes.

Important Mines: While the original Bishopton locality is historic, the most vivid and sought-after microcrystals come from the Joplin District in Missouri, USA, and the Tsumeb Mine in Namibia. In these locations, Greenockite often forms as a coating or as minute, sharp hexagonal pyramids. Finding a crystal large enough to even consider for our “matrix-faceting” technique is a rare victory for any rare stone hunter.

Mineralogical Profile

Description: Greenockite is a cadmium sulfide that crystallizes in the hexagonal system (wurtzite structure). It is relatively soft, sitting at a 3 to 3.5 on the Mohs scale, making it a “collector only” gemstone. It features a resinous to adamantine luster, which gives even the smallest crystals a tremendous amount of “punch” and brilliance. Because of its high refractive index and dispersion, a faceted surface—even on a micro scale—reflects light with a fiery, golden intensity. It is often found as “Cadmium Ochre,” a powdery coating, but the rare, well-formed crystals are what we live for.

Chemical Formula: CdS