[Make it Lady (OP)]

Whilst walking in Scotland we sat and had lunch on the remains of an old lead mine. We picked up a few rocks and saw that some had blue/grey square crystals. The rocks were quite heavy, white on shiney. Firstly were the blue crystals lead? and secondly what were the carrier rocks. Sorry no photo!

[Geezer]

If you were near Elvanfoot, it's a fair bet it was lead.

http://en.wikipedia.org/wiki/Leadhills

[Bored chemist]

It's an even better bet that it was galena- a lead ore.
http://en.wikipedia.org/wiki/Galena

I think most of the galena I have seen was in among quartz, but I'm not sure.
Is there a geologist in the house?

[Bass]

square crystals+blue grey color- no doubt it's galena (lead sulfide).
White carrier rocks (we use the jargon matrix or gangue) most likely quartz, though calcite, barite or anglesite are also possibilities.
Where in Scotland?

[CreativeEnergy]

That's what I was thinking as well...Galena.