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Formula: Cu2MgTe6+O6.6H2O
Oxide, tellurium-bearing mineral
Crystal system: Trigonal
Specific gravity: 3.41 calculated for the ideal formula
Hardness: 3 to 4
Streak: Pale yellow
Colour: Pale yellow to pale orange-yellow
Luminescence: Not fluorescent under long wave or short wave UV
Common impurities: Fe
Environments
Localities
At the type locality, the Centennial Eureka Mine, Eureka, Tintic Mining District, Juab County, Utah, USA, when the
immense dumps were largely removed and processed, a wide variety of mineralised samples was exposed, including
several boulders which contain copper- and
tellurium- bearing assemblages. Leisingite was observed in two of
these boulders and is extremely rare. On the holotype material, it occurs as isolated, or rarely as clusters of,
hexagonal-shaped very thin plates or foliated masses in small vugs of crumbly to drusy white to colourless
quartz. Associated minerals are emerald-green rhombs of
jensenite, leaf-green crystals of
cesbronite and tiny red spherules of
hematite. Additional copper- and
tellurium- bearing
secondary minerals include
mcalpineite,
frankhawthorneite,
xocomecatlite, dugganite
and quetzalcoatlite.
Leisingite is a secondary mineral that formed from the
breakdown of primary
copper- and tellurium- bearing
sulphides. Iron is locally abundant, but the primary source of the magnesium may be derived from the decomposition
of dolomite, which is ubiquitous in the area. The deep water table (about
2,000 feet below the surface) permitted significant oxidation of the original
primary minerals and was the single most important factor in
the formation of the large suite of secondary minerals that
is now present.
Most crystals of leisingite are less than 0.1 mm in diameter and 1 to 2 microns thick
(MM 60.653-657).
Other secondary
tellurium minerals associated with leisingite include
eurekadumpite and utahite,
and leisingite has been found as partial to complete
pseudomorphs after both these minerals
(MinRec 55.2.209, Mindat).
Leisingite from the Centennial Eureka Mine -
Image
At the Upper dumps, North Star Mine, Mammoth, Tintic Mining District, Juab County, Utah, USA, leisingite
occurs as hexagonal yellow plates on a quartz matrix, usually in isolation
but occasionally as groups of intergrown plates. Leisingite crystals in rather unusual colours also have been
found, including green, brown and even pink; the cause of the colouration is unknown
(MinRec 55.2.209).
Leisingite from the Upper Dumps - Image
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