Eckhardite
Eckhardite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula (Ca,Pb)Cu²⁺Te⁶⁺O₅(H₂O).
It crystallizes in the monoclinic crystal system (space group P2_1/n).
Key properties: Mohs hardness 2–3; specific gravity 4.644; Very pale bluish green streak; Vitreous to subadamantine luster; optically biaxial.
IMA symbol Ehd, IMA status: approved, named in 2012.
Found as a secondary mineral in vugs in quartz formed from the partial oxidation of primary sulfides and tellurides during or following the brecciation of quartz veins.
It is found associated with Br-rich chlorargyrite, gold, housleyite, khinite, markcooperite, ottoite.
The mineral was named to honor Colonel Eckhard D. Stuart (b. 1939) of Madison, Mississippi, USA., a mineral collector who has provided numerous samples for research, including this new species.