My husband found what he thought was an interesting rock as we strolled up a BC stream. I broke a piece off and brought it home to photograph. It was easy to break but heavier and more solid than I expected from the look of the outside. The darker green spots are pasty when wet and turn to powder if I scrape at them. What caught my attention was how well a small fridge magnate sticks to it. I don't know much but I don't see any sign of iron nor is there any black to point to magnetite. Can anybody help?

I'm thinking if it were slag there would be quite a bit more mixing than would allow for the consistently spaced blobs of copper.  Copper has a lower melting point than iron thus making it less likely to remain as solid chunks within a molten mass of iron slag.  But this logic relies on the fact that those green blobs were once copper and the matrix being iron.  So, not necessarily ruling out slag, just adding food for thought.

I do believe the green is copper and if you look closely the olive green areas are always associated with the green areas.  So it's possibly oxidized copper making the green or verdigris (http://en.wikipedia.org/wiki/Verdigris) and some sort of copper sulfides making the olive green areas.