Like the title says. Igneous rocks found in nature are extrusions from the earth’s mantle, but there’s no reason that a rock has to come from nature. Could glass be considered a manmade igneous rock?
Most geologic definitions of a rock include something to the effect of “naturally occuring” so no. It’s sort of like how a diamond that gets mined out of the ground is a mineral, but a synthetic diamond isn’t even though they’re essentially the same thing.
To further confuse, volcanic glass isn’t a mineral because it doesn’t have a crystal structure, but it is a rock (usually obsidian) when you find it by itself.
One aspect that defines a rock is that it is naturally formed. Therefore, manmade glass would not qualify.
Obsidian though is a naturally formed glass and it is indeed considered a rock. It’s an extrusive igneous rock, a volcanic glass formed when rapid cooling prevents the constituent material from crystallizing. Often times this indicates some proximity to the surface.
ETA: Beaten to the punch. Like manmade glass, obsidian will display conchoidal fracturing which is what made it a valuable commodity among indians for points and scrapers.
Okay, thanks. Geology was the subject of tonight’s Cub Scout meeting. I’m glad that I didn’t say anything about this one.
I was told at school that glass was an ultra slow moving liquid.
That over a good many years the glass would flow.
Whether this is true or not I have no idea.
Apparenly it’s a myth. The question comes up here with some frequency.
Cecil seems to think otherwise http://www.straightdope.com/columns/read/110/how-come-you-can-see-through-glass
Yeah, if flows, but not in any human appreciable time-span.
Isn’t it true that other ‘true’ solids would also flow over timescales of billions of years?
**Creep!**No, not you - that’s the term for the tendency of a solid material to slowly move or deform permanently under the influence of stresses that are below the yield strength of the material
I understand that solids are also capable of diffusing into one another over very long timescales in contact.
Back to the OP though - I can think of situations where it might be helpful to describe glass as an artificial igneous rock - if, for example, you’re explaining natural processes to young children - and as long as you’re prepared to explain what you mean.
In the same way, pottery could be described as an artificial metamorphic rock. As long as the statement is properly qualified and explained.
What about the slag left over from iron smelting? Would that be classified as an “artificial” igneous rock? It certainly is the result of intense heating. I remember walking with my geography class on a cinder cone in the Craters of the Moon National Park. My professor told us about when he worked at an iron smelting operation and they had huge heaps of leftover slag that were just like volcanic cinder cones.
I’m not sure about rock, but some proposed classifications of soils have a special category for Man-influenced or created soil
Glass is a liquid in the same way that it’s an electrical conductor. Yes, its viscosity isn’t infinite, and neither is its resistivity. But both are so incredibly high that, for almost all practical purposes, they might as well be infinite.