Minerals are naturally occurring solids, stable at ambient/room temperature (25 degrees C), which have a specific chemical formula and atomic structure.
Minerals are composed of a mixture of pure chemical elements which are substances composed of one type of atom and are divided into groups of, metals ( eg – aluminium, copper, iron and lead), non-metals ( eg – carbon, hydrogen, oxygen,) and metalloids (eg – silicon, arsenic).
There are eight elements that form the key components found in the greatest percentage of minerals on Earth. They are listed here in descending order of abundance:-
Oxygen – O, Silicon – Si, Aluminium – Al, Iron – Fe, Magnesium – Mg, Calcium- Ca, Sodium – Na, Potassium – K
Others (this list is not exhaustive) such as Beryllium – Be, Copper – Cu, and Sulphur – S, are also found in various minerals, they and the eight elements listed above, are able to combine with elements, such as Phosphorus – P, Oxygen – O, Hydrogen – H, and Carbon – C, either singularly or grouped together to produce the following classes of minerals:-
Silicates containing Silicon and Oxygen
Sulphides containing Sulphur
Sulphates containing Sulphur and Oxygen
Oxides containing Oxygen
Hydroxides containing Oxygen and Hydrogen
Carbonates containing Carbon and Oxygen
Phosphates containing Phosphorus and Oxygen
Halides containing Fluoride, Chlorine
Borates containing Boron and Oxygen
Therefore the combination of elements and mineral classes, group together to form the wide range of minerals present in the crystalline solids known as crystals.
For example – Silicon (Si) and an oxide (O2) group together to form silicon dioxide which is the mineral present in the crystal Quartz and calcium (Ca)and carbonate (CO3)group together to form calcium carbonate which is the mineral present in the crystal Calcite.
Furthermore, minerals more often that not , occur within solid aggregates of rocks which are defined in three major groups as follows:-
Igneous rock – formed from the solidification of magma or lava
Sedimentary rock – formed by decomposition and precipitation
Metamorphic rock – formed by the transformation or metamorphosis of rock due to changes in heat, pressure or chemical activity.
For example,
The sedimentary rock – Limestone is composed of Calcite and Aragonite which have different crystalline structures but are both calcium carbonates minerals.
The igneous rock – Granite is composed of Quartz, (silicon dioxide), Feldspar, (complex mineral including sodium, potassium, aluminium silicates) and Biotite – black Mica , complex mineral (containing potassium, magnesium, iron, and silicates)
The metamorphic rock Marble is composed of calcite, (calcium carbonate) and Dolomite (calcium magnesium carbonate).
Crystals and Minerals are often found growing on, or embedded within the various types of rock which is then called by its geological term “matrix”.
In this section we have a variety of mineral specimens and crystals that are not otherwise listed under specific categories.