SILICEOUS DEPOSITS FORMED FROM GEOTHERMAL WATER .1. THE MAJOR CONSTITUENTS AND THE EXISTING STATES OF IRON AND ALUMINUM

In the deposition of siliceous material from geothermal water, a relat ionship between chemical compositions of geothermal waters and siliceo us deposits was investigated. The results indicated that iron and alum inium were concentrated into these siliceous deposits. For the chemica l state of the iron in the deposits, some oxides and oxyhydroxides, su lfide and amorphous iron silicate were identified by powder X-ray diff raction and Fe-57 Mossbauer spectroscopy. For the aluminium, two state s were detected by Al-27 MAS NMR: 6-coordinate aluminium (such as alum inium hydroxide) and 4-coordinate aluminium substituting a Si atom sit e in the deposit. In some deposit samples, both 4- and 6-coordinate al uminium were detected, but in others only the former was found.