We find these little milky quartz pebbles in almost every river or loch we rock hunt in. They are stunning when wet, almost opaque. They have a smoky hue for milky quartz. We thought originally that they might be marble, but after polishing a few weeks can confirm that it takes the difficulty to polish which quartz does.
These are from Ayrshire although we have another couple from near Lanark waiting to tumble.
Polished in the tumbler, burnished between stages, ready to go home with you.