Characterization of wheat-rice-stone developed from porphyritic hornblende andesite

Porphyritic hornblende andesite showing wheat-grain stone is known as a “wheat-rice-stone” (WRS) or “mei-fun-shi” (MFS), and has many applications in industry. However, its compositions have not yet been fully investigated. Samples of the porphyritic hornblende andesite from the Tuluanshan Formation (Pleistocene) on the eastern coast range of Taiwan, the Mainland China, and commercial products from Japan were collected in order to characterize their physical and chemical properties, and mineralogical compositions. The major component in the WRS has been identified by X-ray diffraction (XRD) as a smectite. Cation-exchange capacity (CEC) and exchangeable cations of the WRS were related to its water-softening ability. Infrared and elemental analyses indicated that this smectite contained large amounts of water and has a low concentration of nitrogen. Scanning electron micrographs of the porphyritic hornblende andesite displayed a honeycombed polygonal pattern, which has replaced the original bubbled-wall shards. It is because of its water retention capacity rather than its mineral composition that the WRS was used as a fertilizer. The WRS is capable to sorb heavy metals.