Copper clips are unlikely to be pure copper. Also especially silver clips are very unlikely to be pure silver, because both of these metals would be a poor choice for maintaining a tight grip on the cartridge pins. Most cartridge clips are problematic, but their weight or mass makes such a trivial difference that I have never even thought about this as a problem. Why do you bring it up?
How much difference do lower mass cartridge clips make in playback?
My reason for asking is, the normal copper clips fail very easily IME. While they have low mass, I’ve also used the silver clips by JA Mitchell that are easily superior in construction and don’t fail. From a listening standpoint, taking away the differing materials, and the ability of adjusting for VTF, does cartridge clip mass make any significant difference?