In Shadows of Silence, I'm not convinced that the metal is silver. I think it's aluminum.
Remember the Everstorm? Nobody can deny that it was/is magical, but no gemstones were used. There is the possibility of Listeners having gemhearts, but beyond that, we might have some insight into the focus for Roshar. Maybe those Rhythms that we have been hearing about with bronze or briefly in AonDor finally are revealed. I think, maybe, that symmetry is the focus. The glyphs have reflected symmetry. The Void glyphs and the cymatics of the Plains and certain cities use rotational symmetry.