I have recently developed an obsession with a rock I picked up along an abandoned railway in Eldersburg, MD. Initially I assumed that it was just some kind of slag (found it by an old coal hopper), but after spending a few weeks looking at it I burn to know what it's made of and/or how it was produced. I've spent hours online researching rocks and minerals, but I'd be greatful for a more educated guess, or any help determining or describing it's basic properties.
Here's what I can tell you about the rock in question:
-the (very) rough dimensions are 9cm x 6cm x 2.5cm
-it seems very heavy for it's size
-hardness is at least 7 (it easily scratched ceramic and a quartz crystal)
-one side is covered in tiny intersecting translucent brownish crystals that produce bright snowflake-shaped flashes when the rock is moved.