A rather boring photo

Sometimes I wonder if I should only publish a blip when I have a decent photo, rather than resorting to taking photos of rocks that no-one is going to look at....

I actually think this is a rather spectacular rock, but I'm not sure that comes across very well. This is from my most recent New Zealand trip (a country full of marvellous rocks, especially South Island). It was from a beach somewhere between Haast and Fox Glacier, probably closer to the latter. The beach had a sea wall made of huge chunks of this incredibly shiny silver rock - some chunks as big as cars! I have no idea what the rock is and it had obviously been brought in from somewhere else to make the wall. It is very flakey and really looks like silver (but obviously isn't!)

Anyone any ideas what it is?

(I resorted to the rock after fruitlessly chasing bees around the rosemary bush for half an hour)