Felsic Plutonic Rocks for Dummies

Classification of granites

It's been a while since we woke the staff geologist from his slumber to upbraid a freelancer for mangling some bit of earth science, but it happens that today is his (un)lucky day. A staffer was checking for dead links when she ran across one of those fascinating Leaf Group "follow-on": a post that the site's algorithm decided was related. How she happened to get to "Quartz Monzonite Vs. Granite" remains a mystery, but she decided to take a look through and see what Richard Hoyt¹ had to say.

Hoyt, unfortunately, fell victim to Demand Media's minimum word count specification. He started out by introducing his topic and explaining the difference between the two:

"Quartz monzonite... and granite are both granitic rocks... that bear a superficial resemblance to one another... Quartz monzonite contains 5 to 20 percent quartz. Granite contains 20 to 60 percent quartz."

Those thirty-one words encapsulate the difference between the two felsic plutonic rocks and, as such, are all that is necessary to address the topic in the title. Unfortunately, DMS required 300-500 words in three or more sections (plus introduction), meaning Richard had to pad it out. He started in that introduction we mentioned with some questionable statements:

"Granitic rocks are igneous, meaning they were formed by heat under the crust of the earth."

Actually, "igneous" means that that a rock crystallized from a melt, generally within the crust instead of under it. Hoyt had some other goofs in his padding, including

• "Agates are a form of quartz crystals." – Agate is microcrystalline Si0₂, so not "a form of quartz crystals"
• "...quartz monzonite contains K-feldspar, which is similar to quartz..." – No, orthoclase is not "similar to quartz."
• "Some 60 percent of the earth's outer crust is made of feldspar that consists of aluminum silicates plus calcium, potassium, sodium and sometimes barium.." – "Outer" crust? The crust is the outer layer... and barium feldspars are pretty darned rare.
• "Stone Mountain, Georgia, is made of quartz monzonite..." – A geologist wouldn't say it's "made" of quartz monzonite but that it's composed of it.

And so once more we find that a journalism type was trapped by DMS' insistence that they pad any useful content with superfluous factoids. Hoyt had it (mostly) right in the first fifty words or so, but the strain of translating science into language an eighth-grader could comprehend tripped him up. The result? a Dumbass of the Day award for his mantle. Sorry, Dick.

¹ A staffer recognized Hoyt's name and allowed as to how much she's liked his Richard Denson novels...

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