Abstract
Burckhardtite is a new species from the Moctezuma gold mine, Moctezuma, Sonora, Mexico, the type locality for numerous other tellurite species. Burckhardtite occurs as crystalline rosettes less than 0.2mm across, and rarely as single hexagonal or pseudohexagonal crystals up to 50µ with dickite in quartz breccia on the third and second levels of the mine. Minor associated minerals include moctezumite, Pb(UO2)(TeO3)2, zemannite, (Zn,Fe)2(TeO3)3NaxH2−x·nН2O, and barite.
Microprobe analysis gave, in weight percent, SiO2 20.28, TeO2 17.03, Al2O3 5.44, Fe2O3 7.25, Mn2O3 1.18, PbO 45.23, H2O (by difference) 3.59, corresponding to Pb2(Fe,Mn)3+ AlTeSi3O10(OH)2O2·H2O.
Most of the crystalline rosettes have centers of dickite, suggesting an oriented overgrowth. Burckhardtite is inferred to have a sheet structure, and is believed to be monoclinic, pseudohexagonal. X-ray powder diffraction data can be indexed quite well on a С-centered cell with a = 5.21, b = 9.04, с = 12.85A, β = 90°, although a number of minor lines fail to index readily. The principal X-ray diffraction lines, with intensities and Miller indices, are 12.8(9)001; 4.51(2)020,110; 4.26(2)111,003,021; 3.70(9)112,022; 3.11(10)113,023; 2.60(7)200,130; 2.26 (3b)040,220; 2.24(3b)l13,025,115; 2.13(3)222,006,042; 2.00(2)223; 1.840(6)007; 1.590(5)243,153; plus 33 others to 0.793.
Color violet red to pale pink when finely disseminated in clay, streak same but paler. Luster of crystals adamantine to slightly pearly. Cleavage perfect [001]; hardness about 2. Density of crystal rosettes intergrown with clay about 3.2; calculated density, with Z = 2, 4.96. Paramagnetic. Insoluble in hot dilute or concentrated HCl. Optically negative, uniaxial or nearly so; α = 1.82, β = γ= 1.85; X = c. Pleochroism α pale magenta, β and γ carmine red, somewhat variable.
The name is for Carlos Burckhardt (1869-1935), Mexican geologist. Type material is deposited at the Smithsonian Institution (NMNH #144110) and other institutions.
