💎 Crystals
One pattern, billions of times
A diamond and the lead in your pencil are made of the same atom, stacked in different ways.
Look at the flat faces and sharp edges on a crystal.
It looks as if it grew like a plant, or as if someone carved it.
It isn’t alive, and nobody carved it.
It’s one tiny pattern, copied billions of times.
The setup
Start with one unit
Table salt is the easiest crystal to start with. Its pattern is just one sodium and one chlorine, arranged in a little checker. That pair is the unit, and you can stamp it out again and again. On its own it isn’t a crystal yet, but it becomes one as soon as you copy it.
Your turn: drag the slider below. Each step copies the unit more times, and you’ll see a clean square form just from repeating it.
1 unit
The dashed box is one unit. As you add copies, each one goes into the same grid, so the outer edge stays dead straight. That straight edge is a face, and nobody had to shape it.
Your guess
Why is a grain of salt a cube?
Tip some table salt onto a dark plate and look closely, and you’ll see that nearly every grain is a tiny cube. Why do you think that is? Pick an answer before you look.
Grains of table salt are cube-shaped because…
Nobody cuts salt into cubes. The shape comes from inside, because sodium and chlorine lock into a repeating cube pattern, and when trillions of them stack up, the whole grain comes out as a cube. A brick wall works the same way. If you lay identical bricks in a tidy repeating pattern, the face of the wall comes out flat and square without anyone smoothing it.
Every snowflake that has ever fallen is different,
but every one has exactly six arms.
The why
Why snowflakes have six arms
Most snowflakes have six arms, because water molecules lock together in a six-sided pattern. The arms usually match because they all grow in the same air at the same time. Draw in one slice below and watch your drawing get copied into the other five.
Tap or drag anywhere on the disc. You’re only drawing in one sixth of it, and the pattern fills in the rest by copying and mirroring what you draw.
A water molecule is bent, like a wide V. That bend is what makes the molecules link into six-sided rings when they freeze, and six-sided rings build six-armed flakes. The flake is that tiny unit repeated over and over.
The why, again
Flat faces come from the stacking
If nobody polishes a crystal, where do its smooth faces and sharp corners come from? They’re where the neat rows of atoms come to an end. If you stack marbles tidily, the pile finishes in straight, slanted lines by itself. Pick a crystal, then show the faces to see them lying along the last row of atoms.
As you add more atoms, the ragged edge gets closer to a straight line. The face is where a flat wall of atoms stops, and a sharp corner is where two of those walls meet.
A diamond and the lead in your pencil…
…are made of the exact same atom, which is carbon.
The only difference is how the atoms are stacked.
Diamond and graphite
One atom makes two completely different materials
Stacked one way, carbon is the hardest natural material on Earth. Stacked another way, it’s soft enough to smear onto paper. Switch between them below, then try to slide the top layer.
In diamond, every carbon is bonded to four others in a rigid 3-D cage. Nothing can shift, so it’s the hardest natural material there is. In graphite, the carbon is in flat sheets that slide over each other, so bits come off onto your page every time you write. The atoms are identical, and only the arrangement changes.
Salt, sugar, snow, diamonds and the ice on your window…
…are each one small pattern, repeated more times than you could count.
Nobody carved them; their shapes come from the pattern inside.
Pass it on
Once you know this, you’ll see crystals everywhere. The salt and sugar on the table are both stacks of repeating units, and so are a diamond and every other gem. So are the snow outside and the feathery ice that spreads across a cold window, where water molecules line up in the same six-sided pattern over and over. In each one, a tiny arrangement is copied billions of times until it’s big enough for you to see.
Next time someone thinks a crystal was carved, or that a snowflake’s six arms are luck, show them a grain of salt. Explain that it’s a cube because the pattern inside is a cube, starting from the one little unit and working up to the whole grain.
Every crystal is one unit copied billions of times.