#like the only people who argue semantics about this are the crystal woo crowd who insist they're collecting 'crystals' | Explore Tumblr Posts and Blogs

reddpenn · 1 year

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What makes a rock a rock and not a crystal?

Ok SO

A mineral is a naturally occurring non-organic solid with a defined chemical composition and an orderly molecular structure. This means the molecules throughout the entire structure will be exactly the same, and be arranged in a symmetrical, geometric, repeating pattern called a crystal lattice.

Quartz is a mineral. Its chemical formula is silicon dioxide, and its crystal lattice forms a repeating tetrahedron.

Ice is also a mineral. Its chemical formula is dihydrogen monoxide, and its crystal lattice forms a repeating hexagon.

Obsidian is not a mineral. It is a mineraloid, a mineral-like substance. Its chemical composition can vary wildly, and instead of a crystal lattice, its molecules are jumbled up in an amorphous solid, meaning there’s no nice repeating pattern to them.

A crystal is any solid material with a crystal lattice.

All minerals, by definition, have a crystal lattice. So all minerals are crystals! Some things that are NOT minerals are also crystals!

Sugar is a crystal. It has a crystal lattice made from molecules of sucrose. But it is not a mineral because it is organic.

Often, these repeating geometric patterns in the crystal lattice cause the substance to naturally form big geometric structures with distinct faces - such as the points formed by quartz. These larger structures are colloquially also called crystals, and their shape (called a crystal habit) is determined by the shape of the crystal lattice. The same crystal lattice can produce multiple different crystal habits, and it’s all very cool and complicated but I won’t go off on a tangent about it right now.

A substance does not have to form big structures like this to be scientifically considered a crystal. It just needs a crystal lattice!

A rock is a naturally occurring solid aggregate of minerals and/or mineraloids. It can be made of a single mineral, or a bunch of different minerals. But when made from a single mineral, it will not be one solid block of that mineral with an unbroken crystal lattice. Because it is an aggregate, it will be a bunch of micro- to macroscopic grains of that mineral all compacted together, each with their own individual crystal lattices.

Granite is a rock. It is made of grains of minerals such as quartz and feldspar.

Limestone is a rock. It is mostly made of grains of calcite.

So rocks can be made of crystals, but rocks are not crystals - in the same way that a house can be made of bricks, but a house is not a brick!

And this is just a very quick overview of these terms, because the scientific definitions can get increasingly pedantic and there are tons of weird exceptions! It is all very fascinating.

But of course, the word rock also has a colloquial definition, which is just… a chunk of that hard stuff the planet is made of! A mineral, a crystal, a fossil or a bio-organic solid… whatever! This is a rock collection and these are my rocks!

#rock collecting #red pen has cool rocks #talkin' bout rocks #i'm gonna get salty in the tags for a minute about that they're minerals marie meme and how utterly unrealistic it is #because literally everyone in this hobby just calls them rocks #and we all collectively understand that we're using the colloquial definition #it's bizarre to me that the show made that joke because arguing about semantics is honestly kind of a Fake Fan red flag at this point #like the only people who argue semantics about this are the crystal woo crowd who insist they're collecting 'crystals'#they're magical healing crystals marie

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