Hello. I found this rock at a river. Its mate black and has some bubbles in it. It looks like scoria, but its attracted to magnets. Please help!
Hi, a possibility could be magnetite- it can appear the way you've described it. If it has a hardness of 5-6 and has a black streak, this is probably your best bet =)
Another possibility is slag. If its near an iron smelting furnace, that would be an indicator.