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The Grand Reef mine in southeastern Arizona, best known to collectors for superb crystals of linarite, is also the type locality for a unique suite of lead fluoride minerals.
This is also the source of six new lead fluoride minerals (Table 1).
New lead fluoride minerals from the Grand Reef mine.
It is known that the specimens containing the new lead fluoride minerals were all recovered from the bench area that has produced most of the other well-crystallized oxidized minerals at the mine.
None of these minerals were observed in association with the new lead fluoride minerals, although small amounts of gearksutite are present in the matrix surrounding the first rug.
Notably, cerussite was not found on any of the specimens bearing the new lead fluoride minerals.
The absence of cerussite on any of the specimens containing the lead fluoride minerals suggests at least a local dearth of [Mathematical Expression Omitted] in the supergene solutions.
The new lead fluoride minerals are interpreted as resulting from the reaction of late-stage supergene solutions with galena and fluorite.
The evidence suggests the following order of crystallization: galena [right arrow] fluorite [right arrow] quartz [right arrow] anglesite [right arrow] lead fluorides. Among the lead fluorides the order of crystallization based upon the first type specimen (LACMNH 25414) is: grandreefite [right arrow] pseudograndreefite [right arrow] laurelite [right arrow] aravaipaite; the order based upon the second type specimen (LACMNH 39338) is: calcioaravaipaite [right arrow] artroeite.
In this respect, the absence of the secondary calcium fluoride minerals gearksutite and creedite in the vugs with the new lead fluorides, and the presence of essential calcium in only one of the new lead fluorides, calcioaravaipaite, is notable.
The greater abundance of this mineral relative to the other new lead fluorides may also be related to its ability to accommodate chloride.