Hydrothermal – From Geology to Technology (Part 1)

Abstract The term hydrothermal is of geological origin. A great variety of crystals, minerals, ores and rocks have hydrothermal origin and occur as bulk, fine, ultrafine, and nanosized geologic materials. Hydrothermal refers to the action of water and other solvents at elevated temperature and pressure conditions in bringing about changes in the earth crust leading to the formation of rocks, minerals, crystals and ores. It also refers to the post-magmatic and pre-metasomatic stages. In the hydrothermal processes, a variety of volatiles also play an important role in the chemistry and geochemistry of hydrothermal solutions. The origin of a variety of metal deposits in deep-seated submarine hydrothermal ecosystems link with the origin of life on the earth. Today, hydrothermal has become one of the most important experimental methods of understanding the natural systems leading to the crystallization of rocks, minerals and ore deposits. Similarly, it has become one of the environmentally most benign techniques to synthesize a great variety of technological materials with desired functional properties. The technique has advanced so much that under laboratory conditions a wide range of pressure-temperature conditions can be created using specially designed hydrothermal autoclaves, PT sensors and controllers. In the present review, the authors discuss the evolution of hydrothermal process from geology to technology to develop technological materials in different sizes with specific functional properties. Also, the review describes some characteristic natural systems under hydrothermal conditions leading to the formation of some important geologic materials, the influence of different volatiles in the formation of various rocks and mineral deposits. Also the current trends in hydrothermal technology has been discussed with reference to the lowering of temperature and pressure conditions for the synthesis of high melting compounds like alkali rare earth tungstates, vanadates, diamond, etc. in this article.