Kaersutite Root Name Group

The kaersutite root name group minerals are typical for upper mantle rocks. It is common, and even a major constituent of alkali-magmas under high pressures between 25-35 kbar. On surface it can be found as sub mm grains in alkaline volcanic rocks, such as basanites and mugearites, or in alkaline plutonic rocks. Under certain circumstances, titanian amphiboles can also be formed at lower pressures, and it seems as the presence of F- may increase the stability field of kaersutitic amphiboles even at close to atmospheric pressure. Kaersutite crystals can form when the magma fractionates and allow larger crystals to form. It is believed that this is a very slow process, taking maybe thousands of years under constant pressure and temperature to form a 1 cm crystal. The crystal then must be transported to the surface to be frozen as a crystal (megacryst, porfyroblast) in a fine-grained volcanic matrix. Kaersutite minerals may also be formed in volcanic dikes. This is the case for the type locality Qaersut. In these cases, the kaersutite minerals grow rather rapidly, only 25 days is estimated for the up to 4 in. long crystals found near the Hoover Dam in the US. The mechanisms causing the growth of large kaersutite crystals in these dikes has been compared to how pegmatites are formed. The Qaersut occurance has sometimes been referred to as a "kaersutite-pegmatite".