Geol111: Geo Journal Week 02 – Is it a mineral?

This week for my Geology class, we were tasked with finding a mineral, and describe how we identified it.

Listen, I’m not an outdoors person. So when I’m told we need to go and find a mineral, I start looking around for options. And the idea struck me. “Hey, I live a mile from a mining museum, don’t I?” So I looked up their hours, paid the $11 entry fee, and spent a half hour wandering their empty and socially distanced halls, looking at all their cool things.

I’m not going to make this a big post about the museum, because who knows how many of these Geojournals I can get out of it, but here’s some of the many minerals that they had on display.

My real goal of the excursion was the gift shop, where, as I had planned, they sold rock and things. So I picked up a pair. The first was labeled as blood red calcite.

I didn’t pick a very red one, but you can see it’s interesting shapes.

I also bought a much pricier piece of Optical Calcite, which looked a lot clearer in the gift shop than it did when I brought it home.

You can almost see through it. Almost. You can’t make out it’s double refraction as clearly as other samples I’ve seen before.

So how did I know that these are a mineral? I mean, besides the label in the giftshop?

Well, first, observations: It looks vitreous, and has a light color. Not a lot of heft, but I’m not expereienced enough in the practice of guessing density of rocks for that to mean anything for me. I can see it has so nice cleavage, although since I didn’t take this sample myself, I don’t know exactly how reliable it is. I’m reluctant to break it myself.

Also, looking up the mineral, it seems a diluted acid can be used to identify calcite. I tried this, with a mix of vineager and water, but it didn’t seem to do much. Maybe I diluted it too much, or maybe the sample has some sort or clear coating from the place I bought it from to preserve it for customers. I’m not sure.

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