Obsidian

Transcript:

Sarah: And this is everybody's favorite when I'm talking about rocks and minerals. This is obsidian. And I'm gonna actually switch to Minecraft, so here is our Minecraft world, and if I go over here, I have a nice pool of lava over here, and Kim, I want to show you what happens, and I want to see if you have any commentary on it. So I'm going to throw some water there, and then I'm going to clear this water away, if I can. Ah, I'm stuck. No! Everything but the source block. There we go. Okay. All right, so clear the water away, and now I have a little bit of cobblestone and, the rest has turned into Minecraft obsidian.

Kim: Oh, super cool. So the blocks, the red blocks there are lava, is that what those are supposed to be? 

Sarah: Yep, so I had lava, this is a magma block which is a little bit different 

Kim: Magma block, okay, got it. 

Sarah: if I stand on it it'll hurt. 

Kim: Don't stand on it, it's very hot.

Sarah: The lava, when I poured water on the lava, it turned into obsidian.

Kim: Yeah, that's very correct. So what's happening with the lava on the surface of the planet is that it's crystallizing very, very quickly, so if you look at it, you can see it almost looks like glass, and that's exactly what's happening there is that it quenches, or it cools, very, very quickly, and turns into a glass, so that shell kind of feature that has on there is called conchoidal fracture, and that would be the same thing if you were to break a pop bottle, you could see that kind of feature. So it's just, the the atoms don't have enough time to really crystallize in a regular form, and so they form in such a way that's just, kind of, doesn't have any fractures or any way to break very evenly. 

Kim: That's so neat. So when I'm looking at this obsidian, I'm not seeing different colors in it the way I do with the granite or the diorite. 

Kim: That's right, because it's all just one mass of material, silica glass that formed very, very quickly, so it didn't have time to make up those different components, like your granite, or your diorite did deep within the Earth when it had long time to slow cool, so you think of something like, in a, I don't know, in a pressure cooker that has all the time in the world to sort of crystallize, compared to something that is, you know, you pour something wet or water on it, immediately it crystallized really fast, so those are the differences. 

Sarah: So the one other thing that I wanted to know about the obsidian is that, so if I'm in Minecraft and I'm in survival mode, so I don't have unlimited blocks, I have to mine everything myself, if I want to use it, I can only get obsidian if I am using a diamond pickaxe, and it takes forever to get, because it's the hardest block in Minecraft. So does the science match up to the real science there? 

Kim: Certainly basalts and obsidians are quite hard. You know, all the rocks that we've been talking about so far, the diorites, granites, those are all very, very hard rocks. I mean, that's why we make them, you know, counter tops out of them, because they're very durable, and you can cut your vegetables on them without scratching them. So, yeah, I think that is pretty accurate.