HOW ARE MINERALS FORMED?

MINERALS are naturally occuring, inorganic solids, with a characteristic chemical composition, having a regular atomic structure throughout. Man-made industrial diamonds are not considered true minerals. Having said that, there are also some Organic Minerals, such as Amber. Purists are reluctant to call organic minerals minerals, but they satisfy at least three of the criteria for inorganic mineral makeup, and therefore the point is open to debate.

How Many Minerals are there? There are about 4000 listed minerals on this planet but only a relatively few have gained popularity due to their pleasing apperance, often bizarre shapes, exquisite spectrum of colours, and trading value. Minerals are generally composed of more than one element or compound. Those which are made up of only one element are called Native Elements e.g. gold, silver, mercury, copper. The Conquistadores fell in love with New World gold and "liberated" it by the ship-load to fill the coffers of Government and Church in Spain. Silver too, along with Topaz, Tourmaline, Agate, Ruby, Diamond and many other precious rocks and minerals, have been highly prized for as long as Man was first enchanted by their beauty, commercial value and status it imparted to the wearer.

So, just how are minerals formed? Minerals can be formed in a wide variety of geological environments; deep inside volcanos, at the bottoms of deep oceans, deserts, salt lakes and cooling deep deposits of molten rock. Also, under the influence of heat and or pressure, when solutions and gasses holding concentrations of specific elements cool or evaporate, minerals growths are deposited inside rock fissures or voids. These minerals are sometimes forced through as a suspension in water, the water then evaporating leaving the mineral deposits as crystals (e.g. Amethyst) when the rock void is not fully filled or as Agates, when the rock is completely filled. These minerals are only visible when the rock is split open; it takes some skill to decide which rock to crack open! More about that later. An example of such crystal and mineral specimens for collectors are Geodes which are round rocks containing precipitated mineral salts, these being comomonly Agates (caused by mineral salt crystals forming inside Basalt rocks), Amethysts, Quartz, Jasper.

Minerals don't necessarily need heat or pressure to be formed; water saturated with mineral salts can leave deposits (Stalactites) as it drips down from the roof of a cave, forming corresponding Stalagmites directly below, over the centuries, where the drips hit. Eventually both grow to meet each other and thicken over the years. Sometimes, as a novelty, tourists can hang an item on a line at a cave, over which calcium carbonate saturated water runs; over a period of a few months it becomes encased in a hardening deposit of Calcium Carbonate.

THE THREE TYPES OF ROCK. Ok, the basic scene has been set, now let's examine in more detail the different mechanisms involved in mineral formation. All minerals are formed from ROCKS, which are an aggregate or mixture of various minerals and are the basic materials from which a mineral is formed. Rocks can be either:
Igneous - formed due to volcanic activity from the Earth's core.
Metamorphic - formed because of pressure or heat (e.g. tectonic plates colliding) on existing rocks, changing them into another type of rock.
Sedimentary - resulting from the layered compaction of weathered rock materials and/or shells.

Let us examine these rocks a little further:-

IGNEOUS ROCKS(from the Latin ignis - fire) can be further categorised as being