The area of crystals is far too complex to explain in one single blog so I have decided to split it up. In this blog I want to describe how crystals are formed and the different shapes that crystals come in.
How are crystals formed?
When molten magma cools, the minerals that are contained in it crystalise. The process starts with small crystals that grow into larger ones so the longer the cooling process, the larger the crystals. This is why crystals formed deep in the earth will be larger than ones formed in a volcanic eruption where the magma cools quickly. If the resultant material is made of several minerals it is referred to as a rock, if it contains only one mineral, then it is referred to as a mineral.
Igneous Rocks and Minerals
These Igneous rocks and minerals can be classified further depending on where they were formed.
Vulcanites are of volcanic origin and would include pumice stone, basalt and jasper. Fire Opal is also a vulcanite. Sometimes, magma cools too quickly for proper crystal formation. It may run into water for example. The magma is solidified into a glassy substance with Obsidian the best example. Because Obsidian cooled so quickly there is no crystalline structure and is classified as a rock due to it’s very mixed composition. That is why there are so many variations of obsidian including, black, snowflake, mahogany, apache tear, silver sheen and rainbow.
Plutonites are formed deep within the earth and again are further classified. The first minerals form in thick magma and can either sink or float depending on their density. Aventurnine, Peridot and Rose Quartz are formed this way.
Gasses from the magma can penetrate adjoining rocks and minerals such as Apatite, Topaz and Tourmaline can be formed this way.
When the magma is cool enough for water vapour to turn to liquid, further minerals such as Amazonite, fluorite and moonstone are formed out of the substances dissolved in the water.
When liquid water flows it can penetrate more easily into fissures in the surrounding rocks. The minerals left behind in these fissures grow as druse on the walls of the cavity in a formation known as gangue rocks. Large crystals can form due to the slow cooling and this is how many of the most abundant and popular crystals are formed such as Amethyst, Clear Quartz, Chalcedony and Smoky Quartz.
Sedimentary Rocks and Minerals
The action of wind and weather on surface rocks and minerals is called erosion and leads to the second way that rocks are formed. The fine sand that is the eventual result of erosion is finally washed out to sea through rivers where it settles. Large deposits can form and through the pressure of the water above it are compacted to form new rocks. Anhydrite, Calcite, Selenite and some forms of Pyrite are formed this way.
On a smaller scale, surface water can penetrate the rocks closer to the surface. It can dissolve the rocks and release minerals which are then deposited on other deeper rocks above the water table. Azurite, Malachite, Chrysocolla and Turquoise are formed this way. Closer to the water table a different process happens that forms metals such as copper and silver.
Metamorphic Rocks and Minerals
When the plates that form the earth’s crust collide there is huge pressure exerted on the rocks that form the crust. Added to the extreme heat of the magma, these rocks can restructure themselves. The crystalline structure will change so that it is stronger to withstand the pressure and some minerals can also be squeezed out of the rocks which then accumulate and form more resistant minerals. Finally, rocks that are pressed together can exchange minerals to form a boundary layer that is more resistant to the heat and pressure. These new rocks are called Metamorphic.
On a large scale, this metamorphic process will produce crystals such as Kyanite, Garnet, Jade and Serpentine. Marble is also a Metamorphic rock and deposits of Lapis Lazuli and Emerald can be found in marble.
On a smaller scale, the rock around a volcanic chimney for example can be subject to enough pressure to change into metamorphic rock. Ruby and Sapphire are formed this way.
New elements can be added to surrounding rocks through this metamorphic process. Minerals can be leeched out of the rocks and replaced with others which forms minerals such as Charoite, Tiger’s Eye and Rhodonite.
The definition of a crystal is a solid body with a geometrically regular shape and it may be surprising to know that there are only seven different types of crystalline structure. When crystals are formed the lattice is formed to be as close together as possible due to the pressures that surround them when they are formed. Due to this space-saving requirement there is only a limited number of formations that will work. Crystal formations are invariably the same in a large scale as they are small scale so a cubic formation will be cube to the naked eye as well as under a microscope.
Cubic – These will have a square inner structure and include Diamond, Fluorite, Pyrite, Gaernet, Lapis and Magnetite.
Hexagon – These will have a hexagonal inner structure and include Apatite, Aquamarine, Beryl and Emerald.
Trigonal – These will have a triangular inner structure and include Tourmaline, Amethyst, Clear Quartz, Citrine and Ruby.
Tetragonal – These will have rectangular inner structure and include Apophylite and Zircon.
Orthombic – These will have a rhombic inner structure and include Aragonite, Olivine and Topaz.
Monoclinic – These will have inner structures in the shape of a parallelogram and include Selenite, azurite, epidote, moonstone, malachite and jade.
Triclinic – These will have inner structures in the shape of a trapezium and include Amazonite, Kyanite, Labrdorite , Sunstone and Turquoise.
The exception to the rule of crystalline formation is where there is no time for crystals to form. Obsidian is cooled too rapidly because of being dipped in water and Moladavite was smashed into the earth from space. Also some crystals have too many substances mixed together to form a structure as in Amber and Opal.
All information in this blog is thanks to the book Crystal Power, Crystal Healing by Michael Geinger.