Mineralföljden

Mineralföljden, meaning "mineral sequence" in Swedish, refers to the characteristic order in which minerals crystallize from a cooling magma. This concept is fundamental to understanding igneous petrology and the formation of rocks. The most well-known representation of this process is Bowen's Reaction Series, developed by Norman Bowen in the early 20th century.

Bowen's Reaction Series is typically divided into two main branches. The discontinuous branch features minerals that crystallize at progressively lower temperatures and have distinct mineral compositions. It begins with high-temperature minerals like olivine and pyroxene, followed by amphibole, and then mica. Each mineral in this series reacts with the remaining magma as it forms, transforming into the next mineral lower down the series.

The continuous branch, on the other hand, involves minerals of the plagioclase feldspar group. Plagioclase feldspar starts as calcium-rich at high temperatures and gradually becomes more sodium-rich as the magma cools. The composition changes continuously without a drastic change in mineral structure.

As magma cools, the minerals that crystallize first are generally those that are stable at higher temperatures. These early-formed minerals are often denser and may settle out of the magma, influencing the composition of the remaining melt. The specific mineral sequence observed in a rock depends on factors such as the initial composition of the magma, the rate of cooling, and the presence of any fractional crystallization. Understanding mineralföljden helps geologists interpret the thermal history and evolution of magma chambers and the rocks they produce.