crystal
/ KRIS-tuhl /
Look closely at a grain of table salt under a magnifier and you will see a tiny, almost perfect little cube with flat faces and sharp corners. That neatness is no accident. Inside, the atoms are stacked in an orderly, repeating pattern, the way oranges are stacked at a market or tiles are laid on a floor — the same arrangement copied over and over, in every direction. A solid built that way is a crystal.
More precisely, a crystal is a solid whose atoms, ions, or molecules sit in a pattern that repeats regularly throughout the whole material. Pick any atom, walk a fixed step in a fixed direction, and you land on an identical atom in an identical surrounding — and you can keep walking and keep landing on copies, far across the sample. This long-range order is the defining feature. The flat faces and clean angles you see on the outside are simply that hidden inner order showing through to the surface.
Crystals matter because that orderly repetition is what lets us understand and engineer solids at all: it gives a solid sharp, predictable properties, lets X-rays reveal its structure, and underlies metals, gemstones, salt, sugar, and the silicon chips in every phone. The honest caveat is that real crystals are never flawless — they have missing atoms, foreign atoms, and boundaries between mismatched regions called grains. And many everyday solids, like glass or plastic, are not crystals at all: their atoms are frozen in a jumble with no repeating pattern.
Snowflakes are tiny ice crystals. Water molecules freeze into a hexagonal pattern, and that six-fold inner order is why every snowflake — however different in detail — grows with six arms.
Six-armed snowflakes reveal the hexagonal order of ice.
A clear, faceted look is a hint but not proof of crystallinity — a smooth quartz pebble is still a crystal inside, while a sharp-edged shard of glass is not. What defines a crystal is the repeating atomic order, not the outward shape.