How can I tell if the rock is metamorphic, sedimentary, or igneous just by looking at a rock?

February 27, 2005 3 Comments
sterrance asked:

Tags: , , Earth Sciences & Geology
3 Comments to “How can I tell if the rock is metamorphic, sedimentary, or igneous just by looking at a rock?”
  1. Rocknocker says: has pictures and descriptions that will help you.

  2. irene h says:

    im in the same boat.
    Metamorphic- foliated bands, distortion, and intergrown crystals
    Sedimentary- visible particles or sediments, layers, and fossils
    Igneous- large intergrown crystals, glassy texture, porous (vesicular)
    Hope this helps! im stressing over epicenters.

  3. CD says:

    Sedimentary is probably the easiest to identify. It is made up of particles that are (most of the time) visible individually. Some sedimentary rocks have large particles, and some have small particles. Some have particles only visible under a microscope. If you can’t see the particles with the naked eye, rub your hand across it. If it feels grainy, chances are it’s sedimentary. Here’s a good example of what I’m talking about. Another type of sedimentary rock has layers instead of particles. This type of sedimentary rock is even easier to identify than the particle type. It is still made up of particles, but particles that form definite layers, called stratum (more typically referred to using the plural, which is strata) Here’s a good example of sedimentary strata.

    Igneous rock is magma (or lava) that has cooled, hardened, and solidified. It is recognized by it’s generally smooth texture, high mass (basically a rock a certain size will weigh more than you’d expect just by looking at it), and wavy form-remember, it is solidified magma. Here’s what one form of igneous rock looks like.

    Metamorphic rock is hardest to identify. Metamorphic rock is either igneous rock which has fragmented and turned to sediment, then compacted and hardened into sedimentary rock or sedimentary rock that has been subjected to extreme heat (such as a volcano) and melted down. When it cools, you have a metamorphic rock that is similar to igneous rock but is not solidified magma; it is just sedimentary rock that has melted and then cooled. Are you familiar with quartz or diamonds? Both are metamorphic rock. Sedimentary rock that has melted and cooled will have a grainy look to it, feel like igneous rock, will be heavier than normal sedimentary rock, and will not have the wavy composition that igneous rock has. Here’s a picture of sedimentary rock that underwent metamorphism. Igneous rock will that has fractured and then solidified will look like sedimentary rock if viewed from a distance, but up close will have jagged edges on it atypical of sedimentary rock. Most sedimentary rock that is composed of particles has particles that are beadlike. Metamorphic rock that was igneous rock and then fractured and solidified will have particles that are jagged instead of beadlike. They may not feel jagged, but they will look jagged. It will also have less mass than normal igneous rock, and the particles that compose it will feel smooth. Here is a picture of igneous rock that has undergone metamorphism.
    With all metamorphic rock, figuring out if the rock was sedimentary or igneous first will be hard, because sedimentary rock that has been melted down most likely got mixed with igneous rock, so it may confuse you. Igneous rock that has fractured might solidify with other pure sediment, and that will also cause some confusion.

    P.S. Sorry that I gave you the definitions and differences between the rocks-by the time I noticed that you said “I know what the difference is about the rocks” I was already done with my answer, and I didn’t want to sort out what you need and what you don’t, so I left it as it is. Hope you don’t mind.

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