Yes, they have a mineral content that the detector reports as a good target.? You can turn up the discrimination or turn down the sensitivity a little but you will lose a little depth and might cancel out detecting a thin gold ring.?
One beach I detect has a great number of these mixed with the sand.? I've tested my detector on a clean area of ground and balanced the detector.? Then I lay some "hot rocks" down near some thin gold rings of various Kt. and see how the detector behaves.? Many detectorist just tune these rocks out an don't know what targets they are passing over for others to find.
HH,
Sandman