Rock Types, the Dummy Version (Geology Week 1)

The rock cycle

It's time for another theme week here at the Antisocial Network, so we thought we'd put the staff geologist to work collating dumbassery. That's why all week he was heard muttering, "So many dumbasses, so few days!" So without further ado, here's his first nomination for Geology Week: he's Mike Gransbury of Infobarrel.com, caught here telling us his version of "Different rock types explained."

Now, let's be a little kind to start off the week: Mike doesn't actually say anything that's totally off the mark, it's just that his version of how rocks form is a bit on the... simplistic... side, not to mention at times somewhat misleading. But he obviously wrote this rubbish in hopes of getting real money, so it's our considered opinion that he should've gotten it right. Take, for instance, this description of igneous rock genesis:

"Igneous rocks are formed when volcanoes erupt. Hot magma is pushed to the surface from deep underground and it cools to create igneous rock."

Mike should know that volcanism isn't necessary for igneous activity; and should not have stated that magma is "pushed" up: it rises as a result of buoyancy, since melted rock is less dense than the solid rock surrounding it. Moving on to sedimentary rocks, Mike's sketchy information continues:

"In contrast to the almost immediate creation of igneous rocks, sedimentary rock takes millions of years to form. When weathering breaks down older rocks, wind, rain and ice floes can deposit the silt in layers. After several layers have built up the pressure from the weight of the sea or the immense weight of the silt upon silt presses the particles together. As water trickles through the silt the whole thing begins to gel together over time. When the silt is comprised of living matter such as shells or bones limestone is produced."

The staff geologist says, "What makes you think plutonic igneous rocks cool 'almost immediately,' Mike?" He further wonders why Mike's so focused on silt: sediments also include -- oh, we dunno -- sand? and clay? Also, he wants to inform him that limestone isn't created just because "bones" are present. Limestone is created whether or not shells are present; it merely requires that the sediment be mainly calcite. Oh, and by the way, what's this "arkosis" he cites as a sedimentary rock type? Is that an attempt to pluralize "arkose"? And finally, Mike gets to metamorphic rocks:

"Regional metamorphism occurs when movements in the Earth’s crust put extreme pressure on the surrounding rock.

Thermal metamorphism occurs when the extreme temperature of molten lava literally cooks nearby rocks but does not melt them. When this process happens to limestone it becomes marble." For one thing, regional metamorphism requires heat as well as pressure; and for another, that second type of metamorphism isn't called "thermal metamorphism," it's called "contact metamorphism" because the heat source contacts the metamorphosed rock. Also FWIW, marble isn't typically a contact metamorphic product. We had to laugh at some of the extremely specific (and at times odd) rock types Mike cites as examples: lamprophyre for igneous, fossiliferous limestone greywackes [SG says, "That's impossible, since greywacke is a type of sandstone!"] for sedimentary, and spotted slate for metamorphic.

Looks as if this Dumbass of the Day was rooting around in his kid's fifth-grade science book for topics to write about and augmented it with information misinterpreted from Wikipedia. That's a shame: geology ain't rocket science!

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