Quartz vs. Calcite for Dummies (Minerals Week 3)

conchoidal fracture in quartz

Just like mineral grains are (usually) "little things," our research team members are finding that it's often the little things that trip up the freelancing fools to whom we award the DotD. Whereas real freelancing journalists (e.g., Mary Roach) investigate their topics in depth, our candidates often merely skim a wikipedia article or two and reword realistic-sounding phrases¹. It's those details that caught our staffer's eye while perusing "Physical Properties of Calcite & Quartz" at Sciencing.com, the article that earned Patrick Stothers Kwak a nomination.

Oh, Kwak managed to skim the surface of a couple web pages devoted to the two minerals, and he also skimmed the first paragraph of the Wikipedia article about quartz. That, in fact, is where he made his first science boo-boo:

"...quartz is the second most abundant mineral making up the Earth's crust..."

...except that Patrick didn't realize that the same sentence says that "feldspar" is more abundant. Only one problem with that: even G101 students know that there are two feldspars, orthoclase and plagioclase (and plagioclase is further subdivided). Ergo, quartz is the most abundant single mineral.

Kwak copies, rewords, and pastes a lot of details that we're pretty certain he didn't understand such as the notion that

"Both mineral crystal structures fall under the trigonal-crystal-shape category [sic]..."

...which is a bass-ackwards way to say that both minerals are in the trigonal class (quartz is trapezohedral and calcite is scalenohedral). And then there's the discussion of cleavage, where Patrick allows that quartz

"...does not break cleanly and has an indistinct cleavage."

Such are the dangers of simply parroting information you don't understand, Patrick. When a middle-school earth science student or a college pre-law major taking "Rocks for Jocks" asks about the physical properties of calcite and quartz, it's a pretty safe bet that the OQ wants you to tell them that

• Calcite cleaves into well-defined rhombohedra, while quartz exhibits conchoidal fracture (see image above).
• Quartz is stable in (most) acids, while calcite effervesces even in household vinegar.
• Calcite is fluorescent, quartz is not

While hardness data is useful (calcite = 3, quartz = 7 on the Mohs scale), the OQ doesn't want to know the crystal class – especially from someone who doesn't understand that "calcite... exhibits a rhombohedral lattice structure" is utter bull. Even if that were true, how does it "exhibit" the lattice structure? That's at the atomic level!

No, Kwak would have been better off sticking with his business and international relations articles. Dipping into science wasn't a good idea, unless Patrick was actually hoping to collect a Dumbass of the Day award for his work – in which case, he was successful.

¹ If you'd like to see one freelancer's excuse for sloppy work, check out Shanea Patterson's comment here...

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