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thelastspeecher · 10 months

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which rock word has the best artistic pizzazz? I’m a fan of “striation” personally, which I don’t even think is technically a rock word, but the hell do I know

Anyway, actual rock question: how come some rocks by the ocean are like, weirdly porous? they’re just like, 98% hole and 2% rock (I think I’m talking about volcanic porous rock, specifically)

(bonus question, because it’s a Friday: what is your favorite geologist pun?)

"Striation" is a rock-related word! Striations refer to these stripey things present in plagioclase, a kind of feldspar! They're very useful for distinguishing plagioclase from orthoclase, a different kind of feldspar that lacks striations but sometimes has exsolution lamellae (wiggly worm-looking things). The picture below is a close-up of the striations.

In terms of pizzazz-y rock-related words...well I guess "exsolution lamellae" is pretty good. But there's another word that comes to mind, and it's one that my roommate pointed out is Quite Excellent back when we were in college and they were helping me study for geology exams.

Graywacke!

Pronounced "gray-wacky", it refers to a specific kind of sandstone. Here's a picture of a graywacke. It might look just sort of like a rock, but that doesn't make it less pizzazz.

(And for shiggles, here's a picture of some exsolution lamellae in some orthoclase.)

As for your question about porous rocks by the ocean, I have an answer!

You are correct that those particular rocks are volcanic. Multiple kinds of extrusive igneous rocks (rocks that form from lava cooling on the Earth's surface) can have those pores in them, but there are two particular kinds of rocks that always have that texture: pumice and scoria.

We refer to that porous texture as a vesicular texture; the pores and gaps in the rock are vesicles. Extrusive igneous rocks develop a vesicular texture when they cool so quickly that gas bubbles trapped inside the lava cannot escape before the rock fully cools. Pumice and scoria in fact cool so quickly that the lava doesn't even have time to form crystals! That's also the case for obsidian, aka volcanic glass, though obsidian doesn't have that vesicular texture to it.

Fun fact: Pumice is so vesicular, so full of these trapped gas bubbles, that it will float in water! Scoria, though also vesicular, is denser and thus will not float.

Here's a picture of some pumice for you.

And here's some scoria.

Now, my favorite geology pun...

Honestly, I'm very fond of using "schist" (a very sparkly metamorphic rock) instead of "shit". Though that's definitely at least in part due to the fact I didn't swear until halfway through college lmao. I had to get creative with my euphemistic swears.

(And here's some schist for you to admire. I specifically pulled up garnet schist, you're welcome.)

#the word for the sparkly shiny thing schist has going on btw is ''schistosity''#there are a lot of v fun words in geology #but people get distracted by ''cleavage'' and don't pay attention to anything else :/#thank you so much for the geology ask I really enjoyed getting it!#my current job isn't in geology so I miss discussing rocks and whatnot #ask #Anonymous

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