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Formula: Fe3+Te4+2O5(OH)
Tellurite
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
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).
Localities
At Moctezuma, Moctezuma Municipality, Sonora, Mexico, mackeyite occurs abundantly at the San Miguel
prospect and is also reported from the Moctezuma mine. It forms druses of sharp, minute, bottle-green to
olive-green and brownish green crystals with a dull to vitreous lustre, generally less than 1 mm in size and
coating fractures in a quartz-baryte
gangue. The nearly equant, tetragonal crystals resemble octahedrons and
cuboctahedrons. Associations commonly include cliffordite,
emmonsite and schmitterite
(Minrec 55.6.844).
Mackayite from Moctezuma - Image
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).
Mackayite from the Mohawk Mine -
Image
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