“What’s in a name?” asked William Shakespeare in his play Romeo and Juliet. It may also be of interest to explore the origin of some common terms used in geology in an upcoming series.
More than 7,000 terrestrial minerals are known, however only 70 are common and only 10 make up more than 95% of Earth’s crust.
This limited number can be understood if we consider the chemical composition of planet Earth. The most abundant elements here are oxygen, silicon and aluminium – the characteristic elements constituting silicates. Silicates include minerals like quartz (pure silicon-oxygen) and the feldspar-group, a very complex mixture of oxygen, silicon, aluminium and trace elements like sodium, potassium, calcium and more exotic elements like barium.
Feldspars are by far the most common minerals, constituting nearly 58% of all earth´s rocks. They are important crystals in both magmatic (formed by crystallization from molten magma) and metamorphic rocks (formed by alteration of older rocks by heat and pressure over time). It’s only in sedimentary rocks that feldspar are relatively rare, as the crystals easily break (having a perfect cleavage) and tend to quickly react with water.