Don't quote me on this - a son-in-law is a geologist and I should ask him - but I suspect a quartz vein in igneous rock is called an inclusion (hope I'm right). I think the metal ores were associated with these seams. In sandstone that's been fractured and included it looks like this ( http://www.themodernantiquarian.com/post/40644 ) Crap picture - a better view welcome. Splitting a block of granite, in itself, is a gigantic task perhaps - wetted dry wood wedges maybe. I wonder which myths linked the moon with quartz ...