This section provides background information related to the present disclosure which is not necessarily prior art.  Thermoelectric materials may be used for direct conversion of heat to electricity and, thus, can substantially increase the efficiency of energetic processes.  Current state of the art thermoelectric materials are comprised of elements which are in low abundance and often toxic. 
In the past few decades, thermoelectric (TE) materials have been a focus topic in solid-state physics and materials science due to their potential application in waste energy harvesting or Peltier cooling.  The efficiency of thermoelectric materials is evaluated by the figure of merit (ZT=S2σT/κ), where S is the Seebeck coefficient, σ the electric conductivity, T the absolute temperature, and κ thermal conductivity.  For many years, the benchmark for a good thermoelectric material has been ZT of order unity, typified by Bi2Te3 and its alloys which are used commercially in thermoelectric cooling modules. 
One very successful route to improving ZT in bulk solids is reduction of lattice thermal conductivity.  For instance, the notion of “phonon glass/electron crystal (PGEC)” was introduced to describe materials which exhibit lattice thermal conductivity like a glassy or amorphous solid, and electronic properties of a good crystal.  For amorphous or glassy solids, the phonon mean free path approaches one interatomic spacing; a phonon mean free path shorter than one interatomic spacing loses its meaning, and thus this type of thermal transport has been termed “minimal” thermal conductivity.  Unfortunately, poor electrical conductivity in such amorphous solids prevents them from exhibiting high values of figure of merit.  More interesting from the thermoelectric point of view are crystalline solids which exhibit minimal thermal conductivity, due to strong intrinsic phonon scattering.  Examples here include, in addition to the afore-mentioned skutterudites, complex cage structures such as clathrates.  Recently, minimal thermal conductivity was discovered in crystalline rocksalt structure I-V-VI2 compounds (e.g., AgSbTe2), semiconductors typified by the lattice thermal conductivity of a glassy or amorphous system.  These materials exhibit electronic properties characteristic of good crystals and thus have demonstrated good thermoelectric behavior. 
Recently, Skoug and Morelli identified a correlation between minimal thermal conductivity and the existence of a Sb lone pair in Sb-containing ternary semiconductors.  Lone pair electrons induce large lattice anharmonicity that gives rise to thermal resistance.  Using density functional theory calculations, it has been demonstrated explicitly the occurrence of large Grüneisen parameter in Cu3SbSe3 compounds and, using these parameters to calculate phonon scattering rates, were able to quantitatively account for the thermal conductivity using the Debye-Callaway formalism. 
Over the last 15 years, with a more complete understanding of electronic and thermal transport in semiconductors, better control over synthesis methods, and the successful application of nanotechnology, new materials systems with ZT values higher than unity have been discovered and developed, including thin film superlattices, filled skutterudites, and bulk nanostructured chalcogenides.  Unfortunately, many of these new materials are not suitable for large scale application because of complex and costly synthesis procedures, or the use of rare or toxic elements.  A current challenge is the discovery of new thermoelectric materials which are inexpensive, environmental-friendly, easy to synthesize, and comprised of earth-abundant elements. 
The chemical compositions described herein are synthesized from earth abundant materials and in some cases can be extracted in nearly ready-to-use form from the earth's crust.  Furthermore, the compounds are comprised of elements of low atomic mass, such that the density of the compounds is significantly less than state of the art compounds.  These compounds can be used in provide, lightweight, low-cost thermoelectric devices for large scale conversion of heat to electricity. 
According to the present teaching, a thermoelectric device having a pair of conductors and a layer of tetrahedrite disposed between the pair of conductors.  The thermoelectric material can be Cu12-xMxSb4S13. 
According to another teaching, a thermoelectric device is provided having a pair of conductors and a layer of tetrahedrite disposed between the pair of conductors.  The tetrahedrite comprises Cu12-xMxSb4-yAsyS13 where M is selected from the group consisting of Ag, Zn, Fe, Mn, Hg and combinations thereof; 0<x<2; and 0≤y<4. 
According to another teaching a thermoelectric material is presented formed of sintered tetrahedrite having Cu12-xMxSb4-yAsyS13.  M is selected from the group of Zn at a concentration 0<x<2.0, Fe at a concentration 0<x<1.5, and combinations thereof, and 0≤y<4. 
According to another teaching, a thermoelectric device is provided having a pair of conductors, and Cu12-xMxSb4S13 disposed between the conductors, where M is one of Zn and Fe. 
According to another teaching, a thermoelectric device is provided having a pair of conductors.  A p-type thermoelectric material disposed between the conductors, the thermoelectric material being formed of a sintered tetrahedrite powder. 
According to another teaching, method of producing a thermoelectric device is disclosed.  The Method includes forming tetrahedrite comprising Cu12-xMxSb4S13 where M is selected from the group of Zn at a concentration 0<x<2.0, Fe at a concentration 0<x<1.5, and combinations thereof.  The tetrahedrite is ground and hot pressed to form a pellet.  The pellet is disposed between a pair of electrical conductors. 
Further areas of applicability will become apparent from the description provided herein.  The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.