What are minerals?
A mineral is an element or chemical compound that is normally crystalline and that has been formed as a result of geological processes. Examples include quartz, feldspar minerals, calcite, sulfur and the clay minerals such as kaolinite and smectite.
Talc and quartz
Talc and quartz are common minerals, distinguished by different physical properties. Talc is soft, easily scratched and has a greasy feel. Quartz is hard and has a vitreous or glass-like appearance.
Minerals are often used in the production of ceramics.
Properties of minerals
Minerals have a characteristic chemical composition and a highly ordered atomic structure.
Minerals can be readily identified by several physical properties such as hardness, lustre, streak and cleavage. For example, the mineral talc is very soft and easily scratched whereas the mineral quartz is quite hard and not so easily scratched.
Crystal structure
Careful observation of crystal shapes is one of the best ways to classify and distinguish between different minerals.
A crystalline solid is made up of an orderly repeating pattern of constituent atoms, molecules or ions extending in all three spatial dimensions.
A limited number of crystal shapes have been found in nature. There are only 7 groups, or crystal systems, into which all naturally occurring crystals can be placed.
Rocks and minerals
A rock is an aggregate of minerals and need not have a specific chemical composition. Some rocks are predominantly composed of just one mineral. For example, limestone is a sedimentary rock composed almost entirely of the mineral calcite.
Granite
This diagram is a magnified schematic that shows the mineral make-up of the igneous rock known as granite. The main minerals present are feldspars, micas and quartz. The arrangement of these minerals in the rock is purely random.
Other rocks contain many minerals, and the specific minerals in a rock can vary widely. Granite is mainly made up of feldspar minerals, quartz and mica.
When the feldspar minerals present in rock are subjected to weathering, they break down to form clay minerals such as kaolinite (the principal mineral in kaolin clay) and smectite (the principal mineral in bentonite clay).
Ores – mineral rich rocks
Rocks from which minerals are mined for economic purposes are referred to as ores. For example, at the Martha mine in Waihī, the ore body is quartz rock that has small amounts of silver and gold embedded in it. The ore is mined, crushed and treated chemically to release the gold and silver present.
Open pit mine at Waihī
The giant open pit of the Martha gold mine at Waihī in New Zealand’s North Island. Waihī still produces more gold than anywhere else in New Zealand but most of the workings are now underground. This open pit mine is one of the only such mines in the middle of a populated township in the world.
