Quartz vs Feldspar for Dummies - The Freelance Files MMCLXXVII

quartz conchoidal fracture

Imagine, if you will, a freelancer (one with no background in the topic at all) asked to explain the difference between ethanol and methanol. In case you didn't know, they are very different chemicals; one important difference being that ethanol is the alcohol in alcoholic beverages, while methanol (wood alcohol) is poisonous. Our freelancer simply tells us that the difference is "The letter 'm.'" Returning DotD Madhu didn't do quite as bad a job explaining the "Difference Between Quartz and Feldspar" for DifferenceBetween.com... but she came close.

feldspar cleavage

Perhaps with her claimed "BSc (Honours) Degree" in "Biological Sciences," Maddie could have done a better job of explaining the difference between ethanol and methanol, but simply plucking random factoids from the Wikipedia articles for quartz and feldspar doesn't work when you have no idea what those factoids mean. The snarky comment about knowledge is based on a wealth of bogus statements, some of which we'll list below. But first, here's what Madhu claimed to be the main difference between the two:

"[The] key difference between quartz and feldspar is that the major chemical element present in quartz is silicon whereas in feldspar it is aluminum."

Yup, and Maddie said that several times... but it doesn't make it true. For one thing, Madhu never seemed to notice that feldspars are a group of aluminosilicate minerals (orthoclase and plagioclase) differentiated on the basis of the cation present (K, Na, Ca). Nor did she seem to realize that plagioclase is a series of minerals in which varying ratios of calcium and sodium share the cation position.  Heck, Madhu didn't even seem to know that there is igneous quartz!

"Feldspar forms when magma solidifies into igneous rocks. On the other hand, quartz is an oxide of silicon that is abundant on [sic] the earth’s crust."

That "On the other hand" seems to suggest that Madhu doesn't know that there is igneous quartz... or that there is metamorphic and even diagenetic (sedimentary) feldspar. Duh. Here's more of M's bogosity: 

• "...the crystal system of the mineral [quartz] is hexagonal." – Actually, it's trigonal; only at high temperatures is it hexagonal.
• "...quartz crystals are chiral. That means; the quartz exists in two forms as the normal α-quartz and the high-temperature β-quartz " – That's not what chiral means, Madhu. 
• "Feldspar is a mineral compound containing mainly aluminum, silicon and oxygen atoms " – She's confused felspars with andalusite, sillimanite, and kyanite; all of which are made of only Al, Si, and O,,,
• "...we can give [sic] the chemical formula of this mineral as KAlSi3O8¹ – NaAlSi3O8 – CaAl2Si2O8." – No, potassium felspar (orthoclase) is a different mineral while plagioclase feldspars form a series with different amounts of Ca and Na, e.g., labradorite.
• "The mineral streak of feldspar is white..." – The streak of quartz is also white.

"...the common crystal systems [of feldspar] are triclinic and monoclinic structures." – That "structures" bit makes it crystal clear that Madhu has no idea what a crystal system is. "...we can identify a difference between quartz and feldspar from the colors." – People who know what they're talking about know that very few minerals have a distinct color. And finally, Madhu started all this bushwa by calmly intoning that "many people remain confused between these two mineral forms." Well, no, they don't – unless they're ignorant freelancers who copy, reword, and paste material from Wikipedia.

Heck, our Dumbass of the Day didn't even know that quartz has no cleavage while all feldspars have two cleavage directions at right angles (see images above). Given that cleavage is one of the keys to mineral identification, you'd think she'd have mentioned it... if she'd known what "cleavage" is.

¹ The fact that there are three silicon atoms to one aluminum atom puts paid to Madhu's claim that "the major chemical element present... in feldspar... is aluminum."

SI - MINERALS