How do you tell if a rock is sedimentryigneousand medimorphic?

Answer 1

There is more than one way to answer your question, and if you are given a hand sample (like a chunk of rock) sometimes its hard to tell!

Here are some hints that can lead you figure out if a rock is sedimentary, igneous, or metamorphic

If a rock is sedimentary:

it will be composed of grains, or clasts, from other rocks. Sandstones, for example, will be made up of primarily sand grains. Siltstones, clay stones, or grainstones, will have smaller grains that you might not be able to see with the naked eye! Often sedimentary rocks are porous, which means they have little holes that can hold fluids, like water. can you rub the rock and feel grains coming off in your hand? you might have a sedimentary rock. Do you see fossils in the rock? Its most likely sedimentary.

If a rock is igneous;

you need to know what minerals may indicate igneous origin. if the rock is a plutonic igneous rock, it will have large grains, and you will probably see feldspars, biotite, pyroxene, and amphibole. Volcanic rocks will be finer grained, so you need to look for structures and textures that would indicate a volcanic origin. If the rock is massive, i.e, no orientation of grains, and no structures are present, you may have a volcanic igneous rock. If your rock is glassy, like obsidian, you may have a volcanic igneous rock. if your rock has holes in it, like pumice, you may have a volcanic igneous rock

If the rock is metamorphic;

again, you need to look for certain minerals and structures that could point you to this conclusion. If you see chlorite, a harder green mica, you probably have a metamorphic rock. If the rock looks like a sandstone but isn't porous, you have quartzite, a metamorphosed sand stone. If you see foliation (like paper thin layers, perhaps not linear), or deformation structures (like stretched or deformed crystals) there is a good chance you have a metamorphic rock.

While some areas may have more of one type of rock than another area, try not to generalize the area until you know what may be causing these types of rocks.