Siliceous deposits formed from geothermal water I. The major constituents and the existing states of iron and aluminium

In the deposition of siliceous material from geothermal water, a relationship between chemical compositions of geothermal waters and siliceous deposits was investigated. The results indicated that iron and aluminium were concentrated into these siliceous deposits. For the chemical state of the iron in the deposits, some oxides and oxyhydroxides, sulfide and amorphous iron silicate were identified by powder X-ray diffraction and ³⁷Fe Mossbauer spectroscopy. For the aluminium, two states were detected by ²⁷A1 MAS NMR: 6-coordinate aluminium (such as aluminium hydroxide) and 4-coordinate aluminium substituting a Si atom site in the deposit. In some deposit samples, both 4- and 6-coordinate aluminium were detected, but in others only the former was found.