What are Crystals and How do They Form?

The Word 'Crystals' Causes So Much Confusion

The geological definition of a crystal is a naturally occurring solid made up of atoms arranged in a highly ordered, repeating, three-dimensional pattern.

In recent years, the word crystals has been adopted to describe rough or polished rocks and minerals used for their metaphysical healing properties.

This has caused so much confusion when talking about crystals in the geological sense.

In alternative therapies, crystals can refer to anything believed to have healing or spiritual properties. In some articles, even man-made materials like opalite and goldstone are described as crystals.

This overlap in terminology has made it particularly difficult to explain the difference between crystals, rocks and minerals.

It’s not known exactly when the word crystals started being used in this way. What is known is that many ancient cultures, including the Egyptians, Greeks, and Chinese, used certain stones for protection, health, or spiritual rituals. However, they wouldn't have referred to them as crystals.

The modern use of the word likely gained popularity during the New Age movement in the 20th century, when interest in energy, chakras, and alternative healing focused on the natural beauty and symmetry of geological crystals.

Over time, the word became a catch-all for a wide variety of stones used for metaphysical purposes.

In geology, for a naturally occurring, inorganic solid to be called a crystal, it must be crystalline, meaning it's made up of atoms arranged in an orderly repeating pattern that extends in all three dimensions.

When two or more atoms bond together, they form a molecule, and when enough molecules stack together, they form a crystal.

The arrangement of atoms inside a crystal is called a crystal lattice.

The Size of an Atom is Really, Really Small

Atoms are the basic building blocks of everything in the universe, but they’re far too small to be seen, even with most microscopes.

Out of curiosity, I asked AI how many atoms would fit on the head of a pin. Here's what it came up with:
A typical pinhead is about 1.5 millimetres across. The diameter of an atom is roughly 0.1 nanometres, that’s 0.0000000001 metres. Based on those sizes, around 4,216,000,000,000,000,000,000 atoms would fit on a pinhead.

If you're struggling to read that number, it's 42 quintillion, 160 quadrillion, which gives you a sense of just how small atoms are, and how precise and ordered they must be to form a crystal. 

According to the late Professor Stephen Hawking, approximately fourteen billion years ago, the entire universe was the size of a single atom.

How Crystals Form

This diagram shows an example of an orderly, repeating arrangement of atoms inside a crystalline solid.

Crystals usually form when liquids cool and solidify. The slower the cooling process, the more time the crystals have to grow, and the larger they become.

As a liquid cools and solidifies, its particles arrange themselves in an ordered, repeating pattern. This process of crystal formation, called crystallisation, gives a crystal its internal structure. 

Crystals can also form through precipitation. Water can only hold a certain amount of dissolved minerals and salts. When that limit is reached, they can no longer remain dissolved.

At that point, the excess particles come together in a repeating pattern and form solid crystals. This process, where dissolved particles come out of a solution to form a solid, is called precipitation.

Obsidian, a type of volcanic glass, is a non-crystalline solid. This is because the molten lava from which it was produced cooled so fast that there was no time for crystals to grow.

Granite is a rock (not a mineral) known for its large crystals. That's because the magma from which it formed cooled very slowly over millions of years.

Crystals have smooth surfaces known as faces and straight edges. While some, like quartz, are large enough to be seen with the naked eye, others are microscopic.

Some crystals are so small, they're difficult to see even with strong magnification.

Regardless of size, one thing that remains unchanged is that crystals of the same mineral variety always have the same crystal structure. If the structure changes, a different mineral will form.

The smallest piece of quartz is made up of quadrillions of atoms arranged in a crystal lattice. As the atoms come together in an orderly repeating arrangement, they form a crystalline solid.

An atom is the smallest unit of matter that makes up a chemical element.

When the arrangement of atoms within a naturally occurring solid does not form an orderly repeating pattern, the solid is not crystalline. Solids that lack a significant crystal structure are known as mineraloids. 

If a naturally occurring solid is non-crystalline, it's more likely to be classified as a rock, not a mineral. Minerals are made up of crystals, rocks are made up of more than one mineral.

The repeating, three-dimensional arrangement of atoms inside a crystal influences its external shape. The term crystal habit refers to the natural shape of a crystal.

There are seven different types of crystal shape, and every mineral falls into one of these groups. All crystals show symmetry because they’re built from repeating geometric patterns.

Cube-shaped crystals, part of the isometric crystal system, are among the simplest and most common crystal shapes.

One of the most recognisable shapes is hexagonal, often seen in quartz. These six-sided, elongated crystals typically end in a natural termination.

Common Examples of Crystals

Some of the most common examples of crystals include:

Quartz - made up of silicon and oxygen atoms

Halite - better known as table salt, a crystal form of sodium chloride

Calcite - made of calcium carbonate; often forms clear or white crystals

Amethyst - a purple variety of quartz, coloured by trace amounts of iron

Snow - made almost entirely of crystallised water (ice)

Article Pictures

Our first picture, a cluster of quartz crystals, and final picture, gold crystals, are courtesy of Stan Celestian.

The blue, cube-shaped fluorite crystals on quartz is courtesy of Ron Wolf.

Pictures are clickable and redirect to the original photo.