Last week I visited Miami for a conference and while walking around I saw a few women in tank tops or bathing suits with what looked like small crystals on their mid and lower backs. It did not appear to be a typical piercing as there was no visible exit point or visible pin holding it on.
Are these things glued on or embedded in some other fashion? How do they hold on?
You can glue crystals anywhere but that type of piercing is called a ‘dermal anchor’ (technical term is usually subdermal implant). Read the article to find out about the variety of installation processes. My sister has a few.
What he is describing sounds more like a transdermal implant which is also described in your link. These have what looks like little jewels above the skin. A friend of mine has a few of those on one of her forearms.
They could just be glued on as well (cf: bindi, vajazzling) but lower back isn’t a usual place for that, IME.
This reminded me of a dude I saw in the grocery store the other day. Dressed in jeans, t-shirt, ball cap, short hair, clothes sort of dirty like work clothes. He had a big tattoo of a star on the back of his neck. Glued right in the center of it was a big white crystal.