About obsidian, it's essentially glass, can glass be magnetic??

And a funny follow-up. Today I visited one of my favorite antique stores, and found a display of beaded necklaces. I went to pull one off and had to take several others off to get to the one I wanted, with a sales person helping me, and all the sudden all the necklace is stuck together! I realize there was a Blackstone bracelet right below all the necklaces, and as they came off they all got stuck to the same kind of black magnetic stone! It took us a few minutes to untangle them all.