Gemstones are minerals, rocks, or organic matters that have been chosen for their beauty, durability, and rarity and then cut or faceted and polished to make jewelry or other human adornments. Even though most gemstones are hard, some are too soft or fragile to be used in jewelry, so they are often exhibited in museums and sought by collectors.
Gemstones are diverse in their beauty, and many are available in a stunning variety of shades and colors. Most gemstones have little beauty in the rough state, they may look like ordinary rocks or pebbles, but after a skilled cutting and polishing the full color and luster can be seen. Generally, gemstones with clear, medium-tone, intense, and saturated primary colors are most preferred.
Gemstones are formed below the Earth's surface and can sometimes show traces of other minerals, called inclusions. Inclusions can look like small spots or imperfections within the stone. When viewed through a microscope or a 10x loupe, they can give information about the geological environment in which the mineral was formed and its origin. Inclusions can sometimes identify gemstones and even prove whether the stone is natural or synthetic. Some gemstones, such as emeralds, are more likely to have inclusions. Others, such as aquamarine and topaz, generally have very few inclusions or even none at all.
The natural beauty of a gem can be enhanced by the way it is cut. There are two basic kinds of gem cuts: cabochon and faceted. The cabochon cut has a smooth rounded top, usually with a flat base, and it is mainly used for opaque or translucent softer gemstones. Cabochons were the only way in which stones were cut until about the 14th century when faceting was developed. Faceting is the process of cutting a gemstone to improve its beauty by making it reflect more light. The faceted cut has many flat cut surfaces (facets) with an overall shape that might be round, oval, square, and more. Only the harder gemstones can be successfully faceted. A gemstone that has been cut and polished is called a gem, or jewel.
The weight of the gemstone is measured in carats (5 carats = 1 gram). It's important to recognize that some gems are denser than others. For example, a one-carat ruby (very dense) is going to be smaller than a one-carat emerald (less dense). Also, different types of gems that are similar in size may still differ significantly in value.
The hardness of a stone is the only factor in determining gem durability. It indicates the stone’s resistance to scratching and abrasions, or how the surface of the gem will respond to contact with a sharp point. The Mohs Scale rates the hardness of gems and minerals on a relative scale of 1 (softest – Talc) to 10 (hardest – Diamond). Introduced in 1822, the scale originated when Friedrich Mohs chose ten minerals and assigned numbers to them based on the relative ease or difficulty with which one can be scratched by another.
Our planet, which was created about 4.5 billion years ago, is comprised of several layers: the Earth's crust, ranging from 3 to 25 miles deep, the mantle and the inner part of Earth known as the core. Most of the gemstones form as minerals under various conditions in the rocks of the Earth’s crust, while just a few of them form in the mantle. The crust is made up of three kinds of rock, known in geology as igneous, metamorphic and sedimentary rock. All gemstones are mined in the crust. After they are mined, they usually go to a lapidary, which does the final cleaning. This may involve grinding off the matrix or rock, in which the gemstone was buried, and then cutting or faceting and polishing the gemstones. A gemstone that has been cut and polished is called a gem, or jewel.
Gemstones Species and Varieties
Many types of gemstones belong to groups or species which share a common crystal structure and chemical composition. Some of the most important gemstone species include beryl, corundum, garnet, quartz, and tourmaline. Further, each species may have one or more varieties, which have special coloring or features. For instance, the species corundum includes the varieties ruby and sapphire. However, not every gemstone variety belongs to a group, many are unique varieties that don't share properties with any other kind of gem. For instance, peridot, zircon, topaz, and spinel.
Minerals vs. Non-Mineral Gemstones
Although most gemstones are considered minerals, some are also non-mineral. Minerals occur naturally in the Earth’s crust and are defined as inorganic substances that have a characteristic chemical composition and crystalline structures. Minerals are identified by their distinctive properties, such as color, hardness, crystal form, specific gravity, luster, fracture, and tenacity. When a mineral is regarded as rare and exceptionally beautiful, we refer to it as a gemstone (for instance diamond, emerald, ruby, and sapphire). All minerals can be gemstones, but not all gemstones can be minerals.
Also, rocks are comprised of minerals, but minerals are not comprised of rocks. A rock is an inorganic, solid, and natural substance without any specific atomic structure or chemical composition. Its an aggregate composed of two or more minerals which are all firmly locked together to form a hard solid.
Non-mineral or organic gemstones are derived from living organisms like animals and plant life, that have formed into beautiful gemstones due to natural processes — for instance, pearl, coral, amber, ivory, and jet.
Precious vs. Semi-Precious Gemstones
One of the major properties of gemstones is whether they are classified as precious or semi-precious. This is a marketing term designed to make specific stones seem more rare or important than others. Precious gemstones have beauty, durability, and rarity, whereas semi-precious gemstones have only one or two of these qualities. Diamonds, emeralds, rubies, and sapphires are all considered to be precious, and thereby, the most valuable and most desirable. All other gemstones are considered semi-precious.
Natural vs. Synthetic Gemstones
Natural gemstones are found in nature, created deep in the Earth and mined out of it. They are sometimes enhanced, which means they were treated in some way to improve their color or clarity. This often involves heat or delicate chemical processes. Depending on the type and extent of treatment, they can affect the value of the stone.
Synthetic or Lab-created gemstones, on the other hand, are formed in laboratories by human hands and machines. They are chemical, physical, and optically identical to gems found in nature. Of course, lab-created gemstones don't have the rarity of natural gemstones, which is why they are less valuable. Nowadays, synthetic versions of nearly all popular gemstones are available. Some modern synthetic gemstones look more natural and are more difficult to identify, but an experienced jeweler or gemologist can usually detect them.
Simulant or imitation gemstones can be anything that resembles the natural gemstones but does not have the same physical characteristics or chemical composition. These items are usually much less expensive than natural forms. Simulant stones are often made of glass or plastic, and most can be detected easily by a jeweler.