www.alphadictionary.com

Basically a fake precious stone made out of glass, paste, or other material for use in costume jewelry.

So, ARS had an ugly Rhinestone-necklace that described rhinestones as colored glass backed with foil. Then I was like, what "rhine + stone"... WHAT!?! Why the Rhine?

Now I know my great aunt who lived along the Rhine had lots of bits of quartz all over the house which she collected from the Rhine over the decades before the wars. Could this have a root for this word? The quartz wash down from the Alps over the millennial.

According to the Encyclopedia Britannica entry at dictionary.com, rhinestone is:

colourless, faceted glass used in jewelry; also foil-backed or silvered cut glass used to imitate diamonds. Originally used to designate gemstones cut from rock crystal obtained from the Rhine River, Germany, the name historically has been applied to faceted rock crystal in general.