thumb|Covellite (gray) replacing and embaying chalcopyrite (light), polished section from Horn Silver Mine, San Francisco Mining District, [[Utah. Enlarged to 210 diameters. |alt=]]
Covellite (also known as covelline) is a rare copper sulfide mineral with the formula CuS. This indicates that several of covellite's special properties are the result of molecular structure at this level.
As described for copper monosulfide, the assignment of formal oxidation states to the atoms that constitute covellite is deceptive. The formula might seem to suggest the description , . In fact the atomic structure shows that copper and sulfur each adopt two different geometries. However photoelectron spectroscopy, magnetic, and electrical properties all indicate the absence of (d<sup>9</sup>) ions. Thus, the mineral is better described as consisting of and rather than and . Compared to pyrite with a non-closed shell of pairing to form , there are only 2/3 of the sulfur atoms held.
Structure
For a copper sulfide, covellite has a complicated lamellar structure, with alternating layers of CuS and with copper atoms of trigonal planar (uncommon) and tetrahedral coordination respectively. The layers are connected by S-S bonds (based on Van der Waals forces) known as dimers. As a primary mineral, the formation of covellite is restricted to hydrothermal conditions, thus rarely found as such in copper ore deposits or as a volcanic sublimate. Its formation also depends on the state and history of the associated sulfides it was derived from. Experimental evidence shows ammonium metavanadate () to be a potentially important catalyst for covellite's solid state transformation from other copper sulfides. Researchers discovered that covellite can also be produced in the lab under anaerobic conditions by sulfate reducing bacteria at a variety of temperatures. However, further research remains, because although the abundance of covellite may be high, the growth of its crystal size is actually inhibited by physical constraints of the bacteria. It has been experimentally demonstrated that the presence of ammonium vanadates is important in the solid state transformation of other copper sulfides to covellite crystals.
Nicola Covelli (1790-1829), the discoverer of the mineral, was a professor of botany and chemistry though was interested in geology and volcanology, particularly Mount Vesuvius' eruptions. The framework of / allow for an electron excess that facilitate superconduction during particular states, with exceptionally low thermal loss. Material science is now aware of several of covellite's favorable properties and several researchers are intent on synthesizing covellite. Uses of covellite CuS superconductivity research can be seen in lithium battery cathodes, ammonia gas sensors, and solar electric devices with metal chalcogenide thin films.
Lithium ion batteries
Research into alternate cathode material for lithium batteries often examines the complex variations in stoichiometry and tetrahedron layered structure of copper sulfides. Advantages include limited toxicity and low costs. The high electrical conductivity of covellite () and a high theoretical capacity () with flat discharge curves when cycled versus Li+/Li have been determined to play critical roles for capacity.
See also
- List of minerals
- List of minerals named after people