I found this near Valley Forge Pa about a year ago. I broke it in half with a metal tap and a hammer. It took quite a few hits to find that sweet spot- or not so sweet if I shouldn't have broken it. Obviously the flash was on which distorts the color but it is as white/silvery today as it was a year ago. I've since found more pieces that are similar. The heaviest of which is over 4 ounces. Also have some that are black on the outside- reminiscent of a outer crust, yet white inside. There is an abandoned silver mine by my house Phoenixville Pa, (Wheatley). Not sure if this is from there or something completely different. I don't have a proper graduated cylinder for specific gravity, however this stuff is very, very dense. Thanks in advance for taking time out to help.