variscite


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variscite:

see turquoiseturquoise,
hydrous phosphate of aluminum and copper, Al2(OH)3PO4·H2O+Cu, used as a gem. It occurs rarely in crystal form, but is usually cryptocrystalline.
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(1987): "Variscite occurrences in Silurian Formations from Northern Portugal", Comunicacoes dos Servicos Geologicos de Portugal, 73, 1-2, pp.
Precipitation of the minerals strengite or variscite would be possible at this site during the study period given the near-neutral pH of soil (6.9) and groundwater beneath the drainfield (6.7) as well as aerobic conditions (DO: mean 3.2 mg/L) (Robertson et al., 1998).
(From Lindsay, 1979) Mineral Formula Fluoroapatite [Ca.sub.5][(P[O.sub.4]).sub.3]F Hydroxyapatite [Ca.sub.5][(P[O.sub.4]).sub.3]OH Tricalcium phosphate [Ca.sub.3][(P[O.sub.4]).sub.2] Strengite FeP[O.sub.4]-2[H.sub.2]O Variscite AIP[O.sub.4]-2[H.sub.2]O Mineral Solubility Product (M) Fluoroapatite [10.sup.-59] Hydroxyapatite [10.sup.-57] Tricalcium phosphate [10.sup.-26] Strengite [10.sup.-26] Variscite [10.sup.-21] TABLE 10-5 Active S reservoirs.
a) In well drained soils, the principal compounds of Al and Fe phosphates are probably the variscite--barrandite--strengite group: (i) FeP[O.sub.4].2[H.sub.2]O strengite, (ii) ALP[O.sub.4].2[H.sub.2]O variscite;
Based on this concept, the equilibrium constants of AlP[O.sub.4] x 2[H.sub.2]O (variscite) and FeP[O.sub.4] x 2[H.sub.2]O (strengite) shown in Table 1 are used for the present discussion.
Prehistoric mining tools of the variscite mines of Palazuelo de las Cuevas (Zamora) and Pico Centeno (Huelva).
sub.2] Siderite Fe#C[O.sub.3] Oxides Sulfides Cassiterite Sn[O.sub.2] Bornite (Cu sulfide) [Cu#.sub.5] Fe#[S#.sub.4] Hematite [Fe#.sub.2][O.sub.3] Chalcocite [Cu#.sub.2]S# Limonite (bog iron) Fe#O(OH) Chalcopyrite CuFe#[S#.sub.2] x [H.sub.2]O (Fe sulfide) Fe#[S#.sub.2] Magnetite [Fe#.sub.3][O.sub.4] Galena PbS# Shalerite ZnS# Phosphatic Minerals Trace Elements Apatite [Ca#.sub.5](F#,Cl#) Carnotite [K#.sub.2](U[O.sub.2]) [(P#[O.sub.4]).sub.3] [(V#[O.sub.4]).sub.2] Strengite FeP#[O.sub.4] x Fluorite Ca#[F#.sub.2] 2 [H.sub.2]O Variscite AlP#[O.sub.4] x Halite (Rock Salt) NaCl# 2 [H.sub.2]O Note: Essential macro- and micronutrients are indicated with #.
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).
Enfin, cette transformation d'ordre culturel et social semble valoir pour les animaux et pour certaines matieres minerales exploitees a proximite des figures peintes (silex, serpentine, variscite, minerai de cuivre, etc.) (Hameau, 2002, 2006a; Hameau et Painaud, 2009).
Slabs of liddicoatite from Madagascar and variscite nodules from Fairfield, Utah have always had an honored place in the cabinets of mineral collectors.