Thanks, but it's definately not metal. Here's some more clues tho, unweathered it is red. Weathered it is dark grey/black. It is a square shape, about 12" by 12", but it is hung with a single nail at one corner, giving it a diamond pattern on the roof.
They can crack. When they do, it somewhat resembles a grain line, but isn't perfectly in a straight line. In the cracks, you can see what appears to be layers.
There are only a couple of other houses in town with the same type of roofing. It is probably original to the house (80-90 years old), but that can't be confirmed. The round top caps are made of the same material. Thickness is around 1/4", but I haven't measured.
Can anyone confirm that this is indeed slate (or what it might be if not -- asbestos?) Any clues on new pieces to match? Salvage spots for older ones?