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What is the process of crystal formation?

From a scientific perspective, the term “crystal” denotes any solid exhibiting an ordered chemical structure, wherein its components are organized in a precisely arranged pattern, akin to bricks in a wall. These “bricks” may take the form of cubes or more intricate shapes.

As an Earth scientist and educator, my focus often centers on minerals. These are naturally occurring solid substances found in the earth, indivisible into different materials beyond their constituent atoms. Rocks, in turn, comprise various minerals. While all minerals qualify as crystals, it’s essential to note that not all crystals are minerals.

Mineral crystals found in nature are commonly available in rock shops, featuring specimens like pyrite, colloquially known as fool’s gold due to its resemblance to real gold. Additionally, these shops may showcase visually striking, artificially created crystals such as bismuth, a natural element that forms crystals upon melting and subsequent cooling.

The process and reasons behind crystal formation involve the coming together and bonding of similar molecules, creating chemical bonds that function like Velcro among atoms. Crystals do not spontaneously emerge; rather, specific conditions and a nucleation site are required for their growth. This nucleation site could be a rugged edge of a rock or a minute speck of dust that a molecule encounters and adheres to, initiating the chain reaction of crystallization.

In regions at or near the Earth’s surface, numerous molecules are dissolved in water that traverses or flows over the terrain. If there exists a sufficient concentration of like molecules in the water, they will solidify and separate from the water through a process known as precipitation. With a nucleation site present, these molecules will affix to it, instigating the formation of crystals.

An illustration of this process is evident in the growth of rock salt, technically known as the mineral halite. Similarly, another mineral called travertine undergoes this formation process, often creating flat ledges in caves and around hot springs where water triggers chemical reactions between the rock and the surrounding air.

You can create “salt stalactites” at home by cultivating salt crystals on a string, with the string acting as the nucleation site in this experiment. By dissolving Epsom salts in water and immersing a string into the solution, then allowing it to sit for several days, the gradual evaporation of water will leave the Epsom salts behind. Concurrently, salt crystals will precipitate out of the water, fostering the growth of crystals on the string.

Numerous regions in the Earth’s crust experience sufficient heat for rocks to liquefy into magma. As this magma undergoes cooling, mineral crystals form, analogous to water freezing into ice cubes. Notably, these mineral crystals develop at considerably higher temperatures compared to the precipitation of salt or travertine from water.

Crystals, in various forms, offer valuable insights to Earth scientists. The presence of specific mineral crystals in rocks can disclose the rocks’ age, a dating method termed geochronology, signifying the measurement of materials’ age from the Earth. Zircon, renowned for its durability, stands out as a prized mineral crystal for geochronologists. The oldest zircons discovered, originating from Australia, date back approximately 4.3 billion years – nearly as ancient as the Earth itself. Scientists utilize the chemical changes preserved within growing zircons as a reliable “clock” to determine the age of the rocks containing them.

Certain crystals, like zircons, exhibit growth rings reminiscent of tree rings, formed as layers of molecules accumulate during the mineral’s growth. These rings provide scientists with valuable information about the surrounding environment during the crystal’s formation, including variations in pressure, temperature, and magma composition.

On occasion, mineral crystals undergo growth due to shifts in pressure and temperature within the Earth’s crust, transforming rocks from one type to another in a phenomenon known as metamorphism. This transformative process prompts the elements and chemical bonds within the rock to reorganize, forming new crystal structures. Numerous remarkable crystals, such as garnet, kyanite, and staurolite, emerge through this metamorphic growth process.

Incredible Forms When a mineral precipitates from water or crystallizes from magma, its potential size is influenced by the available space for growth. In Mexico, there exists a cave showcasing colossal gypsum crystals, some reaching lengths of 40 feet (12 meters) – comparable to the size of telephone poles.

Mineral crystals that exhibit particularly striking appearances also hold significant value when fashioned into new shapes and polished for jewelry. The highest recorded price for a gemstone was an astounding $71.2 million, paid for the CTF Pink Star diamond. This remarkable gemstone went up for auction in 2017 and was sold in under five minutes.

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