Minerals are the building blocks of rocks. Most rocks are formed of several minerals such as granite with feldspar, quartz and mica. Few rocks consist largely of only one mineral, such as limestone with calcite or quartzite with quartz.
The minerals contained within the rocks are also composed of one or more elements or compounds; they have an ordered internal structure and specific chemical composition.
The key rock-forming minerals are:
silicates, whose key components are silicon, aluminium and oxygen. Examples include feldspars (plagioclase and alkali feldspar), amphibole and pyroxene, quartz, mica, clay minerals and garnet; and
- carbonates,such as calcite (calcium carbonate) and dolomite (calcium magnesium carbonate)
Other groups include phosphates, oxides, sulphides and sulphates.
Common minerals in the three major rock groups are:
Igneous rocks: quartz, feldspar, mica, pyroxene, amphibole and olivine
Sedimentary rocks: quartz, clay minerals, feldspar, calcite and dolomite
Metamorphic rocks: quartz, feldspar, mica, garnet, staurolite and kyanite
The chemical and mineralogical composition of a rock determines the natural supply of nutrients it can provide to vegetation, and therefore has an impact on the choice of rootstock and the varieties grown. The quantity and type of clay minerals, which have different water absorption and ion exchange properties, has a strong influence on soil structure and workability, the behaviour of water in the soil and on the binding and release of nutrients (e.g. potassium and magnesium), as well as on the soil’s susceptibility to erosion.