How Do Crystals Form?
Let us just call crystals ‘nature's little magic tricks’, and it fits well when we describe them. They are believed to pack energies and vibes that can go beyond our human comprehension. And this is what many people have to say about the science of crystal formation:
- “Sure, the science behind how they form is nice to know, but honestly, who cares when you can just bask in their mystical glow?”
- “While the formation process might be a fun fact, the real magic lies in the energy they radiate and the feelings they evoke.”
But knowing about the process of crystals’ formation gives you personal satisfaction and further helps in picking the right crystals. People are drawn to these sparkling beauties, convinced they hold secrets to healing and empowerment. Whether it's for good vibes or just a pretty decoration, we believe that we owe our crystals this much - to understand how they came to be. So, let us move on to how these special rocks are formed.
For the sake of our discussion, we will keep this article limited to:
- How can rocks be (or not be) crystals?
- Crystallisation - how crystals are formed
- Broad categories of crystals as we find them
- Examples
- A crystal versus something that is not
The definition of a “crystal” is determined by the organisation of atoms within it, known as the crystal structure, which is a regular arrangement of atoms in a solid.
And yes, we need not be a geologist to guess that there are solids present which do not have their atomic structure same as crystals. They are formed as polycrystalline structures, having regular arrangements of atoms but not throughout the entire structure. Not all rocks form into crystal. Most inorganic solids are polycrystalline, while amorphous solids, like glass, lack a regular order.
Given this information, we can classify our solids (in this context only) into 3 categories: Crystalline, Polycrystalline and Amorphous.
Science Bit (You can safely ignore this): Microscopically, a single crystal has atoms in a near-perfect periodic arrangement; a polycrystal is composed of many microscopic crystals (called "crystallites" or "grains"); and an amorphous solid (such as glass) has no periodic arrangement even microscopically.
Simple Bit (If you ignored the bit above): There are 3 categories of rocks on the basis of their structure, and are ranked from crystal-like to opposite of crystal-like. A diamond is a crystal, while coal is amorphous.
Note that amorphous solids do not lack in aesthetic beauty either. Whatever nature gives has a magic of its own!
- The journey and formation of a crystal
Now that we have taken the classification of our solids out of the way, we can talk about how a crystal is formed. Their formation involves three steps.
- First, nucleation occurs when molecules or atoms come together in the right way to form a stable aggregate.
- Next is growth, where molecules or atoms are added to the crystal in an orderly fashion.
- Finally, termination halts the growth process. It's fascinating to consider how quickly molecules must arrange themselves on the crystal, even if it's growing slowly at one-tenth of an inch per day. About 100 layers of molecules need to be deposited per second at the crystal surface.
- Types of crystalline rocks
- Igneous rocks are a great example of how crystallization is important in the rock cycle. When magma cools, mineral crystals start to form. The rate of cooling affects the size of the crystals - slow cooling leads to formation of larger crystals, while rapid cooling leads to smaller crystals. This is why some igneous rocks, such as granite, have visible crystals, while others, like basalt, have less visible ones.
- Metamorphic rocks can also undergo crystallization as existing rocks transform due to heat, pressure, or chemical changes. Minerals can recrystallize, grow larger, or change their composition during metamorphism, creating new minerals or altering the appearance and texture of the rock.
- Sedimentary rocks, formed from sediment accumulation, can also experience crystallization. As sediment is buried and compacted, minerals like calcite or silica can cement it together. These minerals can crystallize, forming cement that binds the sediment grains together.
- Examples of crystal in their categories
Igneous: Obsidian and peridot are famous igneous crystals. Quartz family stones like amethyst and citrine and other stones like moonstone, apatite, and tourmaline are also found within igneous rocks.
Metamorphic: Tanzanite, jade, garnet, dolomite, ruby etc.
Sedimentary: Rhodonite, opalite, azurite etc.
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