alunogen


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alunogen

[ə′lün·ə·jən]
(mineralogy)
Al2(SO4)3·18H2O A white mineral occurring as a fibrous incrustation of hydrated aluminum sulfate by volcanic action or decomposition of pyrite. Also known as feather alum; hair salt.
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It can be seen from XRD analysis results, (i) mineral dissolution along with formation of alunogen and bassanite in sulfuric acid (ii) formation of merlinoite, dawsonite and brushite in phosphoric acid, that they can explain an increase in swelling and a decrease in compressibility of soil.
High equilibrium swelling and lesser compressibility of black cotton soil caused by [H.sub.2]S[O.sub.4] and [H.sub.3]P[O.sub.4] contamination is due to (a) replacement of [Ca.sup.++] by [H.sup.+] ions, (b) formation of flocculant fabric, and (c) mineral dissolution and neogenic formations such as alunogen and merlinoite.
Lentschig-Sommer, S.: 1961, Ein Vorkommen von Alunogen Keramohalit im Elbsandsteingebiet.
and Robinson, D.A.: 1998, Weathering of sandstone by alunogen and alum salts.
These equations were used to produce diagrams of amorphous aluminium hydroxide, alunite, alunogen, basaluminite, gibbsite, and jurbanite solubility plus the observed constant [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII], in terms of pAl[(OH).sub.3] activity and sulfuric acid potential.
Figure 5 displays the solubility lines for minerals often associated with acid drainage, such as amorphous aluminium hydroxide, alunite, alunogen, basaluminite, and gibbsite, plus jurbanite and the 'equilibrium' line established by van Breemen (1973) for his experimentally observed constant value for [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII].
Admixtures of alunogen and epsomite are reported, with no details (Eckel, 1997).
Pentahydrite was reported with epsomite in one analysis and with alunogen in another (Hobbs, 1905; Palache et al., 1951; Eckel, 1997).
Alunogen is found as thin colorless plates with elongated pseudohexagonal outline (almost micaceous in aspect), about 0.3 mm in size, associated with magnesiocopiapite on rock surfaces and crevices.