The Sidomulyo zeolitic and Kedungbedah bentonitic tuffs are respectively located in the Gunungkidul and the Boyolali regencies, Indonesia. The study of their mineralogical characteristics was primarily done. The petrographical analysis indicates that the Sidomulyo zeolitic or Kedungbedah bentonitic tuffs is composed of volcanic glass, quartz, plagioclase, and altered minerals. The XRD investigation reveals that the zeolite tuff contains clinoptilolite, mordenite, montmorillonite, plagioclase, quartz, and orthoclase whereas the bentonitic tuff contains montmorillonite, clinoptilolite, illite, dickite, and quartz. The SEM observation of zeolitic tuff displays the presence of clinoptilolite in tabular structure and mordenite in fibrous structure and that of bentonitic tuff mostly presents montmorillonite in webby structure. The activated ion-exchange capacity of the Sidomulyo zeolitic and Kedungbedah bentonitic tuffs are
65.30 mgr.eq.Na2O/100 gram zeolite and 37.6 mg.eq.Na2O/100 gram. The zeolitic tuff dominantly contains clinoptilolite whereas the bentonitic tuff mostly consists of montmorillonite.
Due to their porous structure, the zeolite and bentonite are effectively used as heavy-metal adsorbents: 10g of zeolite in a solution of 250ml can adsorb about 9.80ppm of Cu(II), 10.5ppm of Cr(VI), and 11ppm of Ni(II) and 2.5g of bentonite of a solution of 25ml can adsorb 98% of Cu, 97.2% of Co, 96.8% of Ni, 98.3% of Zn.