Crystallization of magma

More than 95% of all rocks, of which is composed earth crust, formed directly during the crystallization of natural melt, i.e., magma. Crystallization of magma - the phenomenon is very complex. Magma is a mixture of many substances. All these substances have different temperatures crystallization, besides the crystallization temperature of each substance varies depending on the conditions under which the magma is present at the moment, and on what other substances are present in it.

Crystallization of magma - the phenomenon is very complex. Magma is a mixture of many substances

Therefore, during cooling and crystallization, magma is divided into parts: the first in magma arise and begin to grow crystals of the substance whose crystallization temperature is the highest. Usually it turns out that this substance does not yet have time to stand out completely, and the magma has already cooled to the crystallization temperature of the second mineral, and it also begins to stand out in the form of crystals; one after another, alternately or together, influencing each other, other substances begin to crystallize, whereas the previously formed crystals also continue to grow. Finally, divided into heterogeneous areas, all magma hardens. So rocks are formed.

The slower the crystallization of magma occurs, the more crystalline grains of its constituent minerals grow. Therefore, when the crystallization of magma is slow, coarse-grained rocks are formed, and when fast, fine-grained rocks are formed; however, the magnitude of the crystals depends also on many other causes, which in turn affect each other.

If the crystallization of magma occurs not gradually, but suddenly, then, as with any sharp cooling of the melt, non-crystalline minerals or rocks can form. The sudden crystallization of magma is observed during the eruption of a volcano, when hot magma lava emerges from the depths of the earth. Streams of frozen lava on the slopes of volcanoes give rise to non-crystalline, and vitreous rocks, the so-called volcanic glasses. This, for example, is the origin of mineral deposits of obsidian in the Caucasus.

In the crystallizing magma, cracks, channels, voids are sometimes formed, like bubbles in a well-baked bread. Ural stone prospectors called these voids "cellars" or "zanoryshami", and mineralogists - "ghosts". Nothing hinders the growth of crystals here, so gorgeous polyhedra, sometimes reaching grandiose sizes, for example crystals of rock crystal weighing up to one and a half tons, up to 1,5-2 meters in length, feldspar crystals weighing up to one hundred tons with a face area of several tens square meters. Volatile fumes of boron anhydride compounds give the mineral tourmaline, whose trihedral Prisms sometimes represent real columns up to 2-3 meters long.