The Science of Crystals
The geology behind every stone we sell, for anyone who wants to know what a crystal actually is.
A crystal is a mineral with atoms arranged in a repeating, orderly structure, and that structure is the reason it grows into the shapes it does. This guide covers how crystals form geologically, the seven crystal systems that describe their symmetry, how mineralogists classify them by chemistry, and how hardness is measured and why it matters for care.
What Is a Crystal, Exactly?
A crystal is a solid whose atoms are arranged in a repeating, orderly pattern, known as a lattice. That internal order is the entire reason a crystal looks the way it does. The flat faces, the sharp edges, the geometric symmetry, none of it is decorative. It's the outward expression of how the atoms inside are stacked.
Nobody decided a quartz point should taper to six sides. The atoms inside quartz can only pack together in a way that produces six-sided symmetry, so that's what grows, every time, anywhere on Earth quartz forms.
Most, though not all, minerals are crystalline. A few, opal is the best-known example, lack that long-range atomic order and are technically classed as mineraloids rather than true crystals, even though they're treated the same way in practice.
How Do Crystals Actually Form?
Crystals form through four main geological processes: igneous, hydrothermal, metamorphic and sedimentary. Each produces crystals with different characteristics, and knowing which one made a stone tells you something real about it, not just where it came from, but why it looks the way it does.
Igneous formation happens when molten rock cools and solidifies. Hydrothermal formation, the process behind most amethyst, happens when mineral-rich water moves through cracks and cavities, cooling slowly enough to build crystals layer by layer. Metamorphic formation transforms existing minerals under heat and pressure without melting, the origin story for garnet, kyanite, jade and lapis lazuli. Sedimentary formation happens closer to the surface, through weathering and precipitation.
The Seven Crystal Systems
Every crystalline mineral belongs to one of seven crystal systems, cubic, tetragonal, orthorhombic, hexagonal, trigonal, monoclinic and triclinic, based on the symmetry of its internal atomic lattice, not simply its outward appearance.
A mineral's crystal system describes its internal structure; its habit, the shape a specific specimen actually grows into, can vary quite a bit depending on the conditions it formed under, even though the underlying system stays fixed.
How Are Minerals Classified?
Minerals are classified chemically, primarily using the Dana system, into classes based on their dominant chemical component. The major classes include silicates, oxides, carbonates, sulfides, sulfates, halides, phosphates and native elements. Silicates are overwhelmingly the largest class, and include most of what ends up as jewellery: quartz, amethyst and citrine among them.
Hardness and Rarity
Crystal hardness is measured using the Mohs scale, a ten-point relative scratch-resistance scale created in 1812, and it's directly relevant to how a stone should be worn and cared for. Genuine rarity, meanwhile, comes down to geological scarcity, narrow formation conditions and gem-quality yield, not simply how expensive a stone is.
Why Any of This Matters, If You're Not a Geologist
None of this changes what a crystal means to you, or why you were drawn to it. But it does explain something the meaning side of this subject can't: why an amethyst druze catches the light the way it does, why a raw stone looks nothing like its polished counterpart, why some crystals need careful handling and others can be thrown in a bag without a second thought.
We'd say the two sides of this, the geology and the meaning, aren't in competition. A stone can be a genuine record of a specific chemical and physical history, stretching back further than almost anything else you'll ever hold, and still be the thing you reach for on a hard day.
The Science of Crystals, Answered
What is a crystal, scientifically?
A solid with atoms arranged in a repeating, orderly lattice. That internal order produces the flat faces and geometric symmetry visible from the outside.
How do crystals form in nature?
Through four main processes: igneous, hydrothermal, metamorphic, and sedimentary.
What are the seven crystal systems?
Cubic, tetragonal, orthorhombic, hexagonal, trigonal, monoclinic and triclinic, each describing a different type of internal symmetry.
How are minerals classified?
Chemically, using the Dana system, into classes based on dominant chemical component. Silicates are the largest class by far.
What is the Mohs hardness scale?
A ten-point relative scratch-resistance scale, from talc (1) to diamond (10), created in 1812 by Friedrich Mohs.