How do crystals happen? What is a seed crystal? Do they grow?
Scientifically speaking, a crystal is a solid whose atoms are arranged in a repeating, regular geometrical pattern. This usually results in a mineral with lots of straight edges and flat faces, with a specific orientation. There’s a lot of examples of crystals like diamonds, salt, snowflakes and even some kidney stones.
They usually form by a vapor, a solution, or a melt. It begins when certain molecules attract each other in the specific orientation in which they’re most stable, and that attracts more material from the surroundings that gets deposited in the same regular pattern, making the crystal grow.
For example, snowflakes form when water molecules present in the atmosphere clump together around a floating particle under freezing temperatures. Since a water molecule is composed of a positively charged hydrogen atom and two negatively charged oxygen atoms, the most stable configuration that a bunch of water molecules can achieve while connected is a hexagon - each molecule’s position is balanced between the attraction and repulsion promoted by the others. This lattice repeats itself multiple times resulting in a snowflake that grows in a hexagonal layout.
A seed crystal is pretty much what the same says: a seed to make crystals grow. It’s a small crystal that’s inserted into a solution, molten material or vapor containing the same substance as that which it’s made of. The insertion of a small crystal kickstarts the aggregation of the substance to make it grow from there, in a much quicker process than expecting crystals to form naturally - allowing the manufacturing of said crystals on an industrial scale.