Читать книгу Geology and Mineralogy of Gemstones - Karl Wallace, David Turner R. - Страница 29

Gemstones can also be formed through the modification of existing rocks by hot fluids, known as hydrothermal fluids, passing through the Earth’s crust. These hydrothermal fluids contain various dissolved elements and compounds and are often out of chemical equilibrium with the rocks they are passing through. Chemical reactions between the rocks and fluids are common, with the fluids affecting the host rocks and imparting their chemical signatures. When these reactions take place, components from the host rocks can also affect the chemistry of the fluids. These processes are termed metasomatism. Hydrothermal fluids travel from areas of high temperature and/or pressure to areas of low temperature and/or pressure, and so generally move upwards within the crust. They favor geological structures with open or interconnected spaces but can also infiltrate or diffuse through solid rock (Figure 2.13). Cooling and precipitation of their dissolved components into minerals often take the form of veins.