, 5 tweets, 2 min read Read on Twitter
Oolites are so pretty!

Imagine a wee tiny grain. It builds up a coating (usually calcium carbonate) like a geologic pearl, forming an ooid. Then have lots & cement them together into a rock.
Q: But it says orbicular granite??

A: And this is why rock ID from visuals alone is futile! (&/or why you read the museum signs, but it’s Sunday night, that isn’t happening)

Totally diff material & mechanism for same basic aesthetics.
Instead of a grain getting coated (ooids), it’s crystallization cycles.

Mineral 1 precipitates then ~something happens~ (like temp increase to get a lil melty) to round edges, then more crystallizing of mineral 2, repeat-repeat-repeat to grow moar rims. Then crystallize matrix.
What is ridiculously cool about this is that it’s totally different rock types (sedimentary vs igneous), different mechanisms, different minerals, different resulting rock properties, and yet...

It’s still coating spheres & gluing them together.
To be totally obnoxious, the really funny part is that this isn’t a granite. The geochemistry is wrong: Mount Magnet produces granodiorite & tonalite.

Details: mindat.org/loc-245214.html
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