While visiting Harvard’s natural history museum on a trip to Boston, i’ve seen some minerals (or crystals. Not exactly sure of the difference between them) that seems to have naturally formed into near perfect cubes. How is that possible?
It seemed to be most frequent in pyrite.
Thanks in advance!
(Tagged as chemistry, but not sure if it fits)
In: Chemistry
When atoms clump together into a solid, there are two common ways that they settle. There is a crystal structure, and a glassy structure. Glassy structures are chaotic and inconsistent – the atoms are strewn about haphazardly.
As the name would imply, glass is a material like that.
Crystals, however, have a pattern. A repeating structure, like Sodium-Chlorine-Sodium-Chlorine-Sodium-Chlorine. Since the atoms can stick together in different ways, crystal structures can take on [countless patterns](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgEG88lYibXgF7c_owycV-EMpx-v9mH4HgKqcv6pBHYbA8FkXns639Ry5zsfQ5w74lghz701nF78eo_kZez9EwUzLK2prl8g7qvctKPy0xL20QGPm823q_oiptOn7-YWfzxX8X3hQANvBg/s1600/bravais.png).
When the crystal forms, atoms are sticking to it at random. Since the atoms have to snap into place to stay, there’s certain shapes where more or less atoms stick, depending on the crystal structure. For instance, if there’s a side that isn’t lined up flat with one of the ‘flat’ segments of the crystal structure, the atoms may stick more easily there until it becomes flat.
For this to work there must be a single large crystal, not several stuck together, so the atoms usually need a lot of time to slowly clump together and settle snugly into the pattern.
[Pyrite crystal structure](https://upload.wikimedia.org/wikipedia/commons/f/fd/Pyrite_crystal_structure.png). Notice anything?
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