How are gemstones formed? The process of forming mineral crystals

Precious in all cultures and religions, gemstones have sparked the human imagination for thousands of years. During that time, people believed that gemstones had the power to protect, heal, wisdom and even invisibility and give life. But where did gemstones come from?

Most gemstones are made from the crystal forms of different minerals (with the exception of non-mineral organic gemstones such as pearls, corals, and amber). Minerals are formed through a process of naturally occurring chemicals, heat, and/or pressure. The concentration of chemicals determines the structure and color of crystals. The temperature and pressure of crystal formation can affect their size and shape. Most mineral crystals are very tiny, but there are also some that grow large and exquisite enough to be cut into rare and beautiful gemstones. These gemstones can be described as the supreme glory of the mineral world.

While we may not be self-conscious, minerals play an important role in daily life. They form the rocks in the earth's crust, enrich our homes, our roads, and become an important part of all our technology.

Mineral crystals are produced during the formation of three different kinds of rocks, so they are divided into three categories: igneous, metamorphic, and sedimentary rocks.

Igneous Rocks

There is a molten material called magma brewing in the depths of the earth. Magma may originate from the mantle, or it may be due to rising temperatures and/or pressures, or rock melting due to chemical changes. These changes may be caused by the tectonic processes within the earth. The mantle is fluid, and it moves because of the heat from the core of the earth rising to the surface. This creates an electric current within the mantle, presenting a circular pattern of movement. When the magma in the mantle gushes to the surface of the earth, it creates a huge pressure, forcing some liquid rocks to gush to the surface. Once cooled, these rocks will be classified as igneous rocks.

Igneous rocks are divided into two types: invasive and ejection. Intrusive igneous rocks never reach the surface and can only be seen when weathered or exposed to tectonic activity. They are usually dome/bowl-shaped or look like pipes. Dome and bowl-shaped formations are formed due to magma passing through rocks, just like how lava in a lava lamp rises to the top of the lamp and then gathers in the area of resistance. Tubular igneous rocks are formed because magma moves along weak spots within the earth's crust before reaching the surface or areas of rock that cannot be passed through. It then either stops and cools or gathers to form one of the dome/bowl-shaped structures. Crystals are formed when igneous rocks cool down. Intrusive rocks are usually coarse-grained because they cool down slowly and crystals grow. When ejection igneous rocks reach the surface, they are sometimes quite violent. Once they reach the surface, they quickly cool down. This usually creates trapped gases or cavities in the rocks, also known as bubbles.

Gems formed in igneous rocks include feldspar such as tourmaline, aquamarine, topaz, spodumene, heliolite, and celestial stone. Many other gems can be found in igneous rock formations, but they are not products of direct formation from igneous rocks. They are called secondary deposits because they are formed after primary deposits. Many secondary deposits are formed due to hydrothermal processes that introduce high-temperature water into the cavities of existing rocks. Water can transport chemicals into cavities or bubbles, thus forming minerals. Gems found as secondary deposits in igneous rocks include amethyst, larimar gemstones, and fire opals.

Metamorphic Rocks

Metamorphic rocks are formed when an existing rock is affected by intense pressure and/or high temperature, causing its mineral composition, texture, and structure to change. During this process, the rock usually undergoes recrystallization. Recrystallization occurs when the temperature and pressure are strong enough to break the atomic bonds inside the rock, thus changing its structure, while the basic ingredients remain the same. This can be likened to the process of mixing eggs, milk, and fillings together when baking a pie. Before mixing, the ingredients looked varied, but once mixed and heated in the oven, the ingredients of the pie did not change, but their state changed.

Metamorphic rocks can be formed during regional metamorphosis or contact metamorphosis. Regional metamorphic rocks are usually formed deep in the earth due to extreme temperatures close to the mantle and the great pressure of overlying rocks. They can also be formed through large-scale tectonic movements (such as orogenic activities). Contact metamorphic rocks are produced due to contact with lava. Between primitive parent rocks and igneous rocks, there is a metamorphic belt in which metamorphism can exhibit varying degrees of change. Metamorphic rocks close to igneous intrusions may undergo metasomatism due to hydrothermal fluids released when igneous rocks are cooled, which can replace or partially replace the chemical composition within metamorphic rocks.

Metamorphism may cause the formation of metamorphic gems, such as tanzanite, garnet, ruby, sapphire, emerald, spinel, and kyanite, etc. Under metamorphism, these gems may undergo changes in color, structure, or other properties, resulting in a unique appearance and characteristics.

Sedimentary Rocks

Sedimentary rocks are formed by processes on the surface of the earth. They can be composed of other sedimentary rocks, igneous rocks, and metamorphic rocks.

Some sedimentary rocks are deposited from solutions by chemical means, while others may be derived from biochemistry or organic substances, such as calcium carbonate in the shells of past organisms, or from the decomposition of organic tissues of plants and animals. Most sedimentary rocks are formed by eroded rock fragments sticking together. When different types of rocks are exposed to the surface, they will experience erosion called weathering. Weathering refers to the physical rupture of rocks through the physical action of wind, water flow, or ice. These rock fragments are often initialized into rivers and/or oceans. Over time, these fragments will gradually accumulate, and mud and other organic or inorganic elements are compacted together to form hard rocks. Examples of sedimentary rocks include limestone, shale, and sandstone. Some of these gemstone materials, such as coal jade, aragonite, and calcite, also originate from sedimentation.

Surprisingly, many gemstones are actually found in sedimentary deposits after weathering from their original parent rocks. These gemstone materials are found in the sediments of rivers, and these places are called alluvial deposits. They include diamonds, spinels, sapphires, and rubies, etc. In either case, atoms will form complex and orderly structures, which we call crystals. The structure and the chemical composition of minerals together determine the characteristics of crystals, such as shape, hardness, cleavage, refractive index, etc. This is also why the origin of gemstones is so important, because the way they are formed and environmental conditions have an important impact on their physical and chemical characteristics. This provides us with more reasons to cherish these amazing gemstones.