Amongst the other raw-materials the major raw material used in this process of making synthetic granite tiles is processed beach sand garnet. This is a by-product of Indian Rare Earths Ltd., after extracting rate earth oxides from beach sands. 

Garnet are a family of ternary silicate with the general formula A₃ B₂ (SiO₄ )₃. Of  interest here are the deposits formed due to its non-erodable nature of garnets, namely placer deposits of detrital origin. The beaches of Australia and India are among the gifted ones with such placer deposits. Beach sands are processed in port Gregory, Western Australia in a wet concentration plant which can produce 20,000 – 25,000 Tonnes/year. In India the Indian Rare Earths Limited (IREL) have benefaction plants in South-Western and Eastern Coats and they receive beach sands from Manavalakurichi beach in Kanyakumari district of Tamil Nadu. The processed beach sand produced by IREL is around 30,000-40,000 tonnes/year. Besides, there are other agencies who are also producing garnet sand namely M/s.golden Garnet etc. The utilization of such garnet sands is presently limited to a few industries like surface cleaning of materials etc. The average chemical composition and particles size distribution of Indian beach sand garnet is provided in Table I.

Table – I

Particle Size Distribution

The other raw materials used in the process i.e. feldspar, fire clay, inorganic oxides, additives etc. are readily available in the market.

            The beach sand garnet, feldspar, fire clay or other similar clays are mixed together and are processed and pressed in the form of tiles. Sintering temperature usually ranging between 1050^oC to 1100^oC with varying soaking periods. The titles thus made are subjected to grinding and polishing in indigenous polishing machine for mirror-finish granite tiles.

Process: 

            The beach sand garnet is ground to desired fineness. The feldspar and fire clay or some waste materials are ground and sieved through 20 mesh sieve. They are fed into the ball mill along with ground garnet sand and water to make an intimate mixture. The slip thus produced is commonly converted in the form of granual powder using spray drying technique by the present manufacturer of ceramic tiles. However, in order to reduce the initial investment and for the proposed capacity of the plant, the slip is filtered in a filter press to remove excess water. The dried mass is then pressed into shapes at a pressure between 25 and 50 MPa. The pressed tiles and dried at around 110^oC and then fired in an oil fired furnace between 1050^oC and 1100^oC depending on the composition and pig mental oxides used with a soaking period of 1 to 1.5 hrs. Then the fired samples are polished to desired finish.

             The resulting samples are tested for compressive strength, MOR using 3 – point bend test and other physical properties, phase identification using X-ray diffraction etc. The abradibility of the tiles are measured as per BS 1902 Part IA (1986). The microstructure of the samples are evaluated using stereo microscope and optical microscope.