Metals are crystalline in structure, and almost all are polycrystalline. A crystalline structure means that, at the atomic level, atoms are arranged in a repeating, orderly pattern called a lattice. In polycrystalline materials, the structure is made up of many tiny crystallised regions known as grains.
This grainy structure explains why metals often look very different from the distinct, geometric crystals we see in gemstones or even in something like table salt. When a metal cools and solidifies from its liquid state, it forms countless small crystals that grow and eventually connect into a network. Each grain has its own lattice orientation, and together they create the metal’s overall structure.
The size of these grains has a direct effect on a metal’s behaviour:
Smaller grains make the metal stronger, because the increased number of grain boundaries blocks atoms from moving easily.
Larger grains improve conductivity, since fewer boundaries mean atoms and electrons can move more freely.
There are a few exceptions to this polycrystalline rule. For example, turbine blades in jet engines are sometimes made from single crystal metals, which can withstand extreme heat without weakening. And while most metals are crystalline at room temperature, some metallic alloys—or metals cooled very rapidly (like metallic glasses) can become amorphous, meaning they lack a well defined crystalline structure altogether.
Metals in Gemstones
Interestingly, metals aren’t only found in pure metallic form, they are also key to the chemistry of gemstones. Metals influence a gemstone’s formation, structure, and especially its colour.
The purest and most regular atomic arrangement in gemstones is actually found in diamond, which is made entirely of carbon with no metal content at all. But many other gems owe their beauty to the presence of metals:
• Aluminium → found in ruby, sapphire, topaz, and spinel.
• Iron → found in emerald, amethyst, garnet, and peridot.
• Titanium → found in sapphire and alexandrite.
• Chromium → found in ruby, emerald, and alexandrite.
• Copper → found in turquoise, malachite, and azurite.
• Manganese → found in garnet, rhodonite, and some pink sapphires.
And here’s where it gets really fascinating, different metals and their oxidation states are what give gemstones their vivid colours. For example;
• Chromium produces the deep red of rubies and the lush green of emeralds.
• Iron can create blues in sapphires, purples in amethyst, and the olive greens of peridot.
• Titanium combines with iron in sapphire to create the prized velvety blue variety.
• Manganese brings out purples and pinks in garnets and spinel.
• Copper is responsible for the striking blues and greens of turquoise and azurite.
In other words, when you admire the colours of a gemstone, you’re really seeing the hidden chemistry of metals at the atomic scale.
