this post was submitted on 08 Apr 2024
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There's a few levels down from each of those that you can get the broad strokes of fairly easily.
For igneous, you can broadly break it down into extrusive vs intrusive. Basically, did the magma slowly solidify underground, resulting in large grains like in granite, or did it come out in the form of lava that cools rapidly into fine grained or even glassy structures like obsidian. Then there's the other axis of "how much silica is in there?" Really high silica content rocks are called "felsic" rocks. Granite is an example of a felsic intrusive rock, ryolite is an extrusive felsic rock; Basically the same minerals, but way smaller crystals. On the other end of the silica spectrum, there's "mafic" and ultramafic rocks that have less silica and more iron and magnesium. The main example of a mafic rock you might know of is basalt. You can find charts like this one that break things down that way.
Cool diagram! It's interesting how narrow the band of distinguished composition differences is. Anything above 69% is just felsic, and anything below 45% is ultramafic, and hasn't been created any time recently because the Earth has cooled inside.
Structure-wise, for igneous there's various different kinds of intrusions. For metamorphic and sedimentary there's (of course) layers, as well as faults and folds, and pedosphere formations like drumlins. And then there's other kinds of intrusion (if that's the right term) like salt or various kinds of petroleum.
What I'd really love is geological history laid out on a timeline for some specific area. I'd like to be able to picture it all, instead of just looking at isolated examples of a rock or landform.