Mica, element replacement

Indium (0.24 ppm) is similar in abundance to Sb and Cd, whereas T1 (0.7 ppm) is close to Tm and somewhat less abundant than Mo, W and Tb (1.2 ppm). Both elements are chalcophiles (p. 648), indium tending to associate with the similarly sized Zn in its sulfide minerals whilst the larger T1 tends to replace Pb in galena, PbS. Thallium(I) has a similar radius to Rb and so also concentrates with this element in the late magmatic potassium minerals such as feldspars and micas. 

This dispersed element occurs with lead in galena, PbS, where T1+ and Bp+ (or Sb +j replace two Pb +. T1+ replaces the similarly sized K+ and Rb+ (Table 2) occurring in some feldspars and micas. Thallium usually appears in the 1+ oxidation state, but appears as 3+ in the rare mineral Avicennite, TI2O3, found in Central Asia. If Tl(ni) were to appear in the ocean, it would be present as Tl(OH)3(aq). Contrary to the usual principle of hard and soft acids and bases see Hard Soft Acids and Bases), Tl(III) is softer than T1(I).21... 

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