Formula: Fe3+Te4+2O5(OH)
Specific gravity: 4.86
Hardness: 4½
Streak: Pale green
Colour: Pale bottle-green, olive green, brownish green, greenish black; greenish yellow to yellowish green in transmitted light

Hydrothermal environments

Mackayite is a secondary mineral which occurs rarely in the oxidised zone of gold-tellurium deposits, as an alteration product of tellurium. Associated minerals include tellurium, tellurite, emmonsite, rodalquilarite, poughite, cliffordite, sonoraite, pyrite, alunite, baryte and quartz (HOM).


At the type locality, the Mohawk Mine, Goldfield, Goldfield Mining District, Esmeralda county, Nevada, USA, mackayite is associated with tellurium, tellurite, quartz, emmonsite, blakeite, baryte and alunite (Mindat, AM 29.211-225). It is found sparingly in the oxidised zone as a secondary product in vugs and seams in silicified rhyolite and dacite. It is associated with abundant crusts and masses of emmonsite, white powdery masses of tellurite, crystals of alunite, quartz and baryte, limonite and a few reddish-brown crusts of blakeite. One specimen showed native tellurium solidly embedded in quartz, while in the fissures were crystals of mackayite and emmonsite. The sequence of mineralisation would appear to be as follows. The rhyolite or dacite porphyry was brecciated and silicified. The quartz phenocrysts of the original rock are still present in a fine-grained siliceous ground mass. At the same time, small amounts of tellurium and pyrite together with scattered crystals of baryte and alunite were deposited. Baryte seems to have been a little earlier than the alunite (AM 29.211-225).

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