Two new tellurites of iron, mackayite and blakeite, are described, and a third new tellurite is noted. Durdenite of Dana and Wells (1890) from Honduras is shown to be identical with emmonsite of Hillebrand (1885, 1904) from Cripple Creek, Colorado. The name emmonsite is retained for the species. Two new localities for emmonsite, at Silver City, New Mexico, and Goldfield, Nevada, are described. A resume of the descriptions of mackayite and blakeite follows.

Mackayite is a hydrated ferric tellurite of uncertain formula, perhaps Fe2(TeO3)3· xH2O. Tetragonal. Space group probably I/4acd. Cell dimensions: ao= 11.70 ± 0.02, Co=14.95 ± 0.02; ao:co= 1:1.278 (x-ray); 1:1.259 (morphology). Crystals prismatic [001] with a{010}, m{ 110}, g{012} and f{112}; rarely pyramidal {112}. No cleavage. H=4½. G=4.86. Fracture subconchoidal. Luster vitreous. Color peridot- to olive-green and blackish-green. Streak light green. Optically, uniaxial positive (+), with ˉ= 2.19 ± 0.02, ε=2.21 ± 0.02. Faintly pleochroic, with a yellowish-green, e green. Found sparingly at Goldfield, Nevada, as a secondary product in vugs and seams in silicified rhyolite and dacite, associated with emmonsite, tellurite, alunite, barite, quartz, and the new mineral blakeite. Named for John W. Mackay (1831-1902), a mine operator on the Comstock Lode and benefactor of the Mackay School of Mines.

Blakeite occurs in minute amounts as microcrystalline crusts of a deep reddish-brown color. Contains Fe and Te as the only major constituents but the formula is unknown. Nearly or quite isotropic, with n = 2.16±0.02. Named after William P. Blake (1826-1910), a pioneer geologist and mineralogist of the American southwest.

Emmonsite and mackayite on heating to 750°C. fuse and lose water and the residue gives the x-ray powder pattern of artificial anhydrous Fe2(TeO3)3. Blakeite gives in addition faint lines apparently belonging to admixed FeTeO4. X-ray powder diffraction data are given for mackayite, blakeite, emmonsite, artificial Fe2(TeO3)3, and for a new, unnamed, tellurite of iron from Honduras.

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