20 January 2023

Unexpected treasure

I was just walking from one building to the other at work, when I noticed that some flakes had either fallen off a stone in the wall, or had been broken off by some kind of violence. I suppose most people walk past this. But I am a geologist, and I saw and opportunity for seeing a fresh surface! So I picked up the flake. And it looked like an oolitic limestone! I think these are lovely. You don't get to see them very much! I know there are oolitic horizons in the regional Carboniferous limestone, but I couldn't remember seeing anything this beautiful.

In case one wonders; you get ooids if you have bits of carbonate, like shell fragments, rolling around in water that is supersaturated with calcite. The supersaturation makes the calcite precipitate on the substrate of the fragment, and the movement of the water (you might get this in a tidal inlet) makes sure that all sides of the fragment get coated, which in the end results in the round shape. I suppose cave pearls are not that dissimilar in formation.

In the olden days I would've just showed off with this, but the olden days are over. I never have my reading glasses with me at work, so I couldn't look at the flake in close up! So I walked into Jaco's office; I was fairly sure he would have a hand lens. He did! And it sure is an oolitic limestone. I'm keeping that!

It's such a small thing; a nice flake of rock. But I really enjoyed finding that!

Unassuming rock in wall

What it looks like in close-up (use full screen!)

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