Precipitation of the minerals strengite
or variscite would be possible at this site during the study period given the near-neutral pH of soil (6.
1973) observed that strengite
solubilisation was more pronounced under conditions of low pH combined with low redox potential.
Kay was a founding member of the Southern California Micromineralogists Society, and after the German trip she was able to bring, for example, exotic Hagendorf-Sud microspecimens of strunzite, strengite
, hureaulite, phosphophyllite etc.
5, Al and Fe phosphates such as variscite and strengite
were most stable.
Williams and Patrick (1971) observed that crystalline strengite
can be rendered soluble under pH 5 by lowering solution redox potential to values less than -200 mV, which are not normally found in submerged conditions.
From the Boa Vista mine (a phosphate pegmatite) in Galileia, Minas Gerais comes variscite as bright red druses of microcrystals colorfully resting on a matrix of purple strengite
and other rare phosphates.
Mineral forms of P such as strengite
are extremely insoluble and virtually unusable by plants.
Chemical and physical weathering, along with a reduction in soil pH from the leaching of basic cations, give rise to the many forms of P secondary minerals, such as the Fe-enriched strengite
and the Al-enriched variscite (Lindsay 1979).
It occurs in partly oxidized gray orthoclase-quartzpyrite rock, following earlier strengite
and followed by an unidentified green member of the rockbridgeite family (Eckel, 1997).
These include sicklerite, purpurite, hureaulite, phosphosiderite, strengite
, stewartite, eosphorite, robertsite, mitridatite, jahnsite, fairfieldite, hopeite, and pseudomalachite.
Thin fracture coatings and vug linings of botryoidal, dark green to black dufrenite have been observed very rarely, associated with radial sprays of strengite
, minute cubic crystals of pharmacosiderite, and local sprays of meurigite.
Summing up their work on Sapucaia phosphates, Lindberg and Pecora (1958) listed their apatite, bermanite, childrenite, gordonite, heterosite, hureaulite, leucophosphite, lipscombite, metastrengite (= phosphosiderite), montebrasite, roscherite, saleeite, strengite
, triphylite, variscite and vivianite as having been positively identified, in addition to the new species.