Lex

one time i got a huge pile of stuff and he STILL said it and i said "dude, you would not be satisfied with all the riches of heaven!!" and he said "i don't even get a commission. i just love doing this."

There are two kinds of rock "descriptions" when you're trying to name a rock: Rock Groups, and Rock Descriptors. Geologists often use them interchangeably, but they're very different.

Rock Groups are the overall chemical compositions of a rock that give you a ballpark idea. This is typically what people think when they say 'type' of rock and most geologists will ID it. Limestone tells you that the rock is predominantly CaCO3 and was likely formed in a shallow ocean environment. Sandstone tells you that the rock is a bunch of little sand grains.

However, this is sandstone. ^ And this is also sandstone. ^

To differentiate the two, geologists start adding descriptors. So a full "name" for a sedimentary rock might be, "Red, poorly-sorted, well-rounded quartz arenite sandstone"

Translation: A red sandstone where grains are roughly the same size, fairly round, and of primarily quartz composition.

Volcanic rocks are often much harder, because it's based on percentage of minerals in the rock. "Granite" is a rock grouping most people know, but really defines "a rock high in silica and aluminum and low in iron and magnesium with large crystals that took a while to cool." Whereas, "Basalt" would be "a rock high in iron and magnesium, lower in silica and aluminum with crystals too small to see with the naked eye that cooled quickly."

Whereas a full name would be, maybe, "Porphyryitic Granodiorite" = "rock of granodioritic composition on the diagram, with some large crystals in a fine-grained matrix". Or "Green Vesicular Propylitically-Altered Basalt" = "Green fine-grained rock with holes that had a lot of iron and magnesium but that was taken out and replaced with a lot of calcium."

Igneous, Sedimentary, Metamorphic are the boxes that we put rocks in because they describe the kind of environment we're looking for. And then the first level beneath that is, (for ign.) how large are the crystals and what color is the rock; (for sed) what are the parts of the rock made of, and (for meta.) what texture is the rock?

Those classifications are more that enough to overwhelm a beginner because each answer to the question corresponds with a physical environment of the earth. You have ~roughly~ six igneous rocks to correlate, five sedimentary rocks (+/- 2 depending on how mean the teacher wants to be), and six metamorphic rocks, (also +/- 2 depending on educational cruelty).

Geology is, for this reason, the most philosophical science, because there are 'rules' to follow, in the sense that technically if you have over 90% quartz in an igneous rock, you're supposed to call it a Quartzolite. But unless you sit and count out every single fucking crystal in an 1x1 inch representative rock sample (which some people DO and I applaud them for), you don't know that it's over 90% quartz. Or a sedimentary rock might change intermittently over several meters from a sandstone to a cobblestone because it had channels running through it. What do you call the rock then? A sandstone? or a cobblestone?

It'd be sadistic to make people just introduced to the concept of time over place and "sandstones can indicate a river or a desert environment, while cobblestones can mean a river or rockfall environment" to- "you could kind of name this anything sandstoney-sedimentary; the presumed interpretation doesn't change, but add these descriptors to make sure the people who come after you know you saw these cobblestones and weren't ignoring them; or it'll chaos at the conference bar because one guy saw some angle on the cobblestones here and you didn't."

losing time