Giant crystals from our mine in Victoria Australia
Gem Citrine crystal
Giant Crystals form very slowly
Giant Crystals are quite rare, When magma cools, crystals form because the solution is super-saturated with respect to some minerals. If the magma cools quickly, the crystals do not have much time to form, so they are very small. If the magma cools slowly, then the crystals have enough time to grow and become large. Some granites contain minerals which are up to one meter (3 ft) across!
Crystals are orderly arrangements of pure substances. For example, diamonds are pure carbon, and quartz is pure silicon dioxide. Crystals form as their component atoms move closer and closer together. This can occur as pressure and temperature decrease, or as a solvent evaporates. Once the atoms begin to associate, their geometry and chemical activity determine the shape of the crystals that form. In general, the size of the crystals will depend on the amount of substance present in a given space, and how quickly the atoms can associate. The slower the association, the larger the crystal.
The fantastic crystal structures in geodes, or hydrolites, form as water evaporates from the internal spaces of the stones. However, most crystals are found in rocks that have a volcanic origin. As the super hot molten rock – called magma – cools, different substances will crystallize out. Sometimes very large crystals, weighing up to several tons, can be made as magma slowly cools below the surface of the Earth.
Crystals also can be formed when land masses move. The crust of the earth can buckle and fold, raising mountains and creating new faults. Such stresses create great pressures and temperatures that can change the crystal structures in rocks. These rocks are called metamorphic rocks. Crystals in metamorphic rocks are generally pretty small.
Crystal World has a large inventory of giant crystals from Australia and other countries.
Sometimes, a rock will contain both aphanitic and phaneritic crystals in it. This means that something truly odd happened to the magma before it was erupted. Since we know that large crystals need time to grow, the magma must have spent some time deep underground. But the smaller crystals mean that the rest of the cooling happened very quickly. If a rock has both crystal types, it means that the mamga spent some time in a magma chamber, where the large crystals grew, then was violently erupted onto the surface, where the small crystals were formed. A good example of this is the Colbert Rhyolite in the Arbuckle Mountains of Oklahoma.