These rhinestones with crossed channel silver setting are vintage to very old, from about the 1930s to the 1970s. Mostly crystal with a colored coating at the back to lend them their various colors. the facetting adds the sparkle.

Crossed-back setting  = Claws hold the crystal and 2 crossed channels at the back are for sewing on, or passing thin wires / strong thread through for

There are 2 kinds offered here:

1- Facetted at the front and flat at the back.

2- Facetted at the front and at the back with a pointed or conical back. This results in a diamond-like sparkle.