Nonmetals, Industrial Minerals and Gemstones

Abstract

Nonmetallic and industrial minerals are the essential raw materials for a number of industries. Gemstones have been in demand throughout much of human history. Nonmetallic and industrial minerals are divided into the following groups: refractory minerals, fertilizer minerals, minerals used in cement industry, chemical industry, electrical industry, glass and ceramic industry, abrasive industry, and those used as fillers and pigments, and as building stones. Refractory minerals are those that can, besides withstanding high temperatures (up to ~1500 ℃), endure thermal and mechanical shocks. They are mostly used in the internal lining of metallurgical furnaces. They are categorized into three sub-types: acid, neutral, and basic, depending on their relationship with various kinds of slags and furnace linings. The acidic variety includes quartz, fire clay , ball clay , kyanite, sillimanite; the neutral variety includes chromite, graphite and asbestos, while the basic variety comprises magnesite, dolomite, and bauxite. India has got a reasonably good reserve of refractory minerals, being the largest repository of alumino-silicate minerals. The principal fertilizer mineral is a phosphate (phosphorite, apatite), now used mostly for the manufacture of superphosphate using H₂SO₄. Bulk of phosphate mineral deposits are sedimentary (-diagenetic) in origin. A number of phosphate deposits are in Rajasthan, followed by Madhya Pradesh, Uttarakhand, and West Bengal. However, India imports phosphate ore from West Asia. K-bearing fertilizer minerals occur in large quantities in Nagaur-Ganganagar basin, Rajasthan. Portland cement requires limestone, clay, and some 5% gypsum for its manufacture. India has a satisfactory reserve of these raw materials. Plaster of Paris is made with gypsum. Minerals needed in chemical industry are native sulfur, Fe-sulfides, barite, and fluorite. In fact, >80% of barite mined is used in making “heavy mud” for the oil drilling industry while fluorite’s main use is as flux in metallurgical processes. Minerals used for thermo-electrical insulators comprise muscovite mica, asbestos, steatite, talc, vermiculite, and pyrophyllite. Li is extractable from lepidolite. Micas are available aplenty from the mica-pegmatites of Bihar, Rajasthan, and Andhra Pradesh. Glass and ceramic materials are in great demand for making quite a few things necessary for our everyday life, as well as in industries. We have necessary reserves of quartz, feldspar, and clays for this industry. Industrial abrasives vary in hardness and may be natural or manufactured. Hard abrasives are more manufactured these days. Natural hard mineral matter for abrasives includes diamond (industrial variety or bort) and corundum. Natural soft abrasive materials are many. Building stones comprise granite gneisses, granites, marble, limestone, sandstone and slate. Charnockites and khondalites also make good building stones. Quality of a building stone is determined by its beauty and durability. India’s annual business in this trade exceeds INR 10 billion. The most precious gemstones found in India are diamond, followed by ruby, sapphire and emerald. Diamonds are obtained from kimberlites and lamproites and related coarse sediments in central and south India. Ruby, sapphires, and emerald are found in the Kashmir Himalaya, Rajasthan, and Karnataka. Precious quality zircon (gomed) is found in the beach sands of peninsular India. The bulk of India’s need of gemstones is, however, satisfied by other countries including South Africa, Sri Lanka, and Myanmar.