I was a "rockhound" back in my teens (40-50 years ago), so my knowledge of Minerology is now a bit rusty. To me, those objects look like either Galena (lead ore) or Iron Pyrite ("fool's-gold"). Galena is silvery, and Pyrite is of course usually "pale golden-ish." Due to the vagaries of color accuracy in digital photography, I can't be sure about the color of yours. Their shape looks cubic-based, and appears silvery in the photo, so I lean toward them being Galena.
Another clue is weight. Galena's Specific Gravity is 7.2 to 7.6, just slightly higher than cast-iron. Pyrite rates 4.9 to 5.1, significantly lighter than iron.
You could do what is called a "streak test." (No jokes from you other oldtimers, please.) Pyrite makes a Greenish-black to brownish-black streak on unglazed ceramics (like the underside of a toilet-tank's lid), and Galena's streak is lead-grey.
I forgot to mention... if my information doesn't give you the answer, there is a person named Dustedyou here at TreasureNet who posted an invitation for anybody who has a rock they want identified to contact him. Here is the link to that invitation: http://www.treasurenet.com/forums/h...ified-post-here-gimme-good-picture-3-4-a.html