Carnelian is a brownish-red mineral commonly used as a semi-precious gemstone. Similar to carnelian is sard, which is generally harder and darker. Both carnelian and sard are varieties of the silica mineral chalcedony colored by impurities of iron oxide.
About 20 years ago "carnelian" was scarce.
I was told it was because what we had thought was carnelian,
the beads of one color, was really Brazilian onyx that was dyed to be that color.
Maybe under an electron microscope it's all the same.
European countries had cracked down on the dye used and
it took a while to come up with a new and acceptable dye.
I believe the "goldfish" carnelian, the multicolored ones, are natural.