Pronounced with a hard C (like kalcedony). Whatever.
All precious gemstones are some form of silica, which makes up most of the dirt of the Earths crust. Although I'm not a geologist, and was too lazy to study science in school, I sometimes spout junk that just ain't true. When it comes to chalcedony, maybe I'm right, maybe I'm wrong.
Anyway, there's a lot of this stuff out in the desert. I watched a Youtube video of a guy chipping it out of a mountain a couple miles north of the city. I've also found it nearly everywhere I've ever hiked.
Typically white, but often has interesting swirls and bands. Some coloring gets in occasionally. For someone like me who will try to cab a turd if given the opportunity, I've been pleasantly surprised by some of the chalcedony I've cut.
Note that chalcedony is also the matrix that precious fire agate can be found in.