THE MINERAL EMPLECTITE

• Chemistry: CuBiS₂, Copper Bismuth Sulfide
• Class: Sulfides
• Subclass: Sulfosalts
• Uses: As mineral specimens and as a very minor ore of copper and bismuth.
• Specimens

Emplectite is a another interesting sulfosalt mineral; a unique and diverse group of minerals to collect. The sulfosalts are unique because they have an enigmatic structure. They seem to have a structure where the semi-metals, such as bismuth in emplectite's case, act as the central metal ion in a structural unit with the sulfurs such as the ion group BiS₄^-5. This is then analogous to the basic structural units of the other groups of minerals such as SO₄^-2, for the sulfates, for example. It was this analogy that was used to justify the name sulfosalts since these minerals would theoretically be the "salts" of a "sulfo-acid" just as CaSO₄, is the salt of hydrosulfuric acid, H₂SO₄. But this theory of formation for the sulfosalts is not supported by crystallographic studies, yet the name sulfosalts is still used. Another way to think of sulfosalts is as a double sulfide where the formula for emplectite could be written as CuS-BiS.

Emplectite forms in hydrothermal veins with other bismuth and copper minerals. Unfortunately emplectite is a difficult mineral to distinguish from other gray, acicular to massive, dense sulfosalts with a black streak. Its name is from the Greek word for "interwoven" in allusion to its penchant for being crystallized within and around other similar minerals. Emplectite has also been known as "cuprobismutite". Emplectite is isostructural (same structure) with another sulfosalt called chalcostibite. Chalcostibite has a formula of CuSbS₂.

PHYSICAL CHARACTERISTICS:

• Color is iron gray, yellow gray, whitish gray to tin white.
• Luster is metallic.
• Transparency: Crystals are opaque.
• Crystal System: Orthorhombic; 2/m 2/m 2/m.
• Crystal Habits include prismatic to acicular crystals, often in radial aggregates; embedded and massive forms are also common.
• Cleavage: Perfect in one direction (prismatic).
• Fracture: Uneven.
• Hardness is 2
• Specific Gravity is 6.3 - 6.4 (heavier than average for metallic minerals)
• Streak is black.
• Other Characteristics: Specimens will develop a yellow tarnish.
• Associated Minerals include quartz, barite, wittichenite, chalcopyrite and skutterudite.
• Notable Occurrences include the type locality of Tannenbaum, Schwarzenberg, Saxony; Germany; Turkey; Chile; Campbell Mine, Cochise County, Arizona and Colorado, USA.
• Best Field Indicators are crystal habit, cleavage, softness, color and density.