Greisenisoituminen

Greisenization is a metamorphic process that occurs in rocks, particularly granites, at high temperatures and pressures. It is characterized by the formation of a fine-grained, dark, and often glassy rock known as greisen. This process typically takes place at temperatures between 300°C and 500°C and pressures of about 3-5 kilobars. Greisenization is often associated with the late stages of magmatic activity and is commonly found in areas where granitic intrusions have been subjected to significant metamorphism.

The term "greisen" originates from the German word for "hard," reflecting the rock's hardness and resistance to weathering. Greisen is typically composed of quartz, feldspar, and various accessory minerals such as tourmaline, topaz, and cassiterite. The formation of greisen involves the alteration of the original granite minerals, with the release of volatile components like water, carbon dioxide, and fluorine. These volatiles migrate through the rock, leading to the precipitation of new minerals and the development of the characteristic greisen texture.

Greisenization can have significant economic implications, as it is often associated with the formation of valuable mineral deposits, such as tin, tungsten, and lithium. The process can also affect the physical properties of the rock, making it more resistant to weathering and erosion. Understanding greisenization is crucial for geologists and mineral explorers, as it provides insights into the geological history of an area and the potential for mineral resources.