27d (edited) • 🪨 The Daily Rock
Texas Rocks: Limestone!
Hi everyone,
I’m in Texas right now, specifically San Antonio. The geology isn’t crazy diverse, but the rocks that do show off are particularly cool.
South Texas is covered in Limestone. Around 500 million years ago, most of the southern US was covered by a warm shallow sea. It retreated overtime and left millions of crustaceans, coral and dead sea life exposed. Over time these fossilized while compacting and turned into a rich layer of rock. This is what we call Limestone.
Limestone has some easy to identify features, like porousness, but can be confidently confirmed by an acid test. A couple drops of diluted hydrochloric acid (hydrogen peroxide is a common household acid that can work) causes the carbonate in the limestone to dissolve. While dissolving it fizzes and bubbles. When it does that, you’ve got limestone!
The acid test proves carbonate is in the makeup of the rock. Carbonate is a derivative of organic matter. So if you get fizzing on your rock, that’s a good indication that part of the rock was once a living thing!
Anyway, here’s some cool pictures of very porous limestone just hanging out in my parent’s neighborhood.
Q: any limestone in your collection? Do the acid test and find out!
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Texas Rocks: Limestone!
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