Gneiss

Transcript: Part 1

Sarah: So I have some rocks that we can look at, and maybe we can talk about those. So let me just change the cameras. All right. So we have our granite friend from before, but we have a new rock.

Kim: That's a "gneiss" looking rock you have there.  

Sarah: It's a nice piece of gneiss. 

Kim: It is a nice gneiss, sometimes people say. So yeah, so you can see the rock on the one side there that has nice crystals. You know, there's some black material, there's some white material, there's some pink material. And then on the other side there, they've gone into, sort of, these layers, because there's been some pressure, some temperature, and kind of changed it a little bit into a rock that looks a little different.

Sarah: That's really cool. So this is a transformed version of this?

Kim: Pretty much. That's a good way of putting it. So it's just a little bit denser, a little bit, I guess, kind of, maybe, squished a little bit, and changed into a different rock. 

Sarah: That's super cool. Why does it go into layers like this? 

Kim: Well if you think of, you know, if you tried to put a whole bunch of -- what's round that we can talk about? Like pillows. Like some, you know, just pillows off your bed, and you threw a whole bunch of them on the floor, and then you started piling up a whole bunch of people on top of it, the big fluffy pillows are gonna go flat, right?  Like, they're gonna start to squish after you've piled up 20 people on top of each other, right?

It's kind of the same idea. As these rocks go deeper into the Earth, get a little bit of heat, because once you have some pressure, if you have all those 20 people on there, the bottom person's going to be a little squished, and probably a little hot from all that stuff on top. It's kind of the same idea. It's just this process of burial, of change, of heat and pressure, and things start to squish out into flatter layers.

Transcript: Part 2

Sarah: We've talked about this before, but now it is actually in the game because I put it there. We now have some gneiss that I made. 

Kim: That is some beautiful gneiss. So yes, so gneiss is a metamorphic rock, and it's more of a texture than anything. It forms these beautiful bands of light and dark. The different minerals get almost squished and pulled apart into these long long lines. Instead of having round grains, we have these long skinny features in the rock that have just basically squished the minerals down into a flat, flat, flat, flat, flat.

Sarah: And I notice again it does have a lot of the same colors as granite.

Kim: It does. So a lot of gneisses are made up of feldspars and a biotite, so sort of that, you know, those darks the lights, and quartz, so we have some of the same components that we see in granite, but they've just been pulled out squished into these lines instead of having the big large crystals that we see in granite.