Duloe stone circle in Cornwall is all quartz. I found a single quartz stone at the site of old Chapel longbarrow on fyfield down recently. PeteG
I'm going to Duloe later this year.
I've also seen a stone with a fantastic streak of quarz in this year to. Part of a circle. . but I can't remember which one! (I've been on a circle-fest this year!). I'll check me notes . . .