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Relationship between Igneous, Sedimentary & Metamorphic Rocks, Rock or…

- - - - Fossil presence: Looking for fossils or organic material in sedimentary rocks provides information about its type and history. Coal is a sedimentary rock made of plant fossils--bioclastic rocks are characterized by fossils pressed between other sediments
      - Grain size: Some sedimentary rocks have visible grains, we can often look at their relative size to see how sediments may have been transported
      - Crystal structure: Rocks like gypsum have crystals present (crystalline) while others like limestone often do not (amorphous)
      - Clastic vs Chemical: Sedimentary rocks can be an assortment of older rock particles (clastic, like shale), or the result of chemical precipitation that reacted with preexisting rocks (chemical, like chert)
  - - - Mineral composition (Mafic or Felsic): Mafic minerals are made mainly of elements like magnesium and iron. Felsic minerals are often comprised of quartz and feldspars, containing more silicates. Usually identifiable by color, dark-toned rocks are commonly mafic in composition while light-toned rocks are likely felsic. Periodotite, containing very little silica, is an ultra-mafic mineral.
      - Cooling history: Magma cools either slowly (forms large, distinct crystals within rock) or quickly (forms tiny, less structured crystals within rock)
      - Origin: This refers to whether the magma cooled and solidified in the Earth's crust (extrusive rocks, like andesite, basalt or rhyolite) or above the surface as lava (intrusive rocks, like granite, diorite, or gabbro)
      - Texture:
        Phaneritic: large, coarse crystals Pegmatitic: very large, connected crystals
        Aphanitic: microscopic crystalline grains, smooth to the naked eye Porphyritic: made of fine-grained rock combined with larger crystals (phenocrysts)
        Vesicular: often rough, the rock contains many holes from trapped gasses being released as magma solidifies