The night of July 4th while sitting in my den, my next door neighbor began setting off fireworks. At one point, I heard a thud on the roof. I forgot about it until this Saturday...when I was on the roof cleaning the gutters. I found what I believe to be the source of the thud. The first and second image is the actual object. It feels a little like brick mortar, but not as heavy. The third picture, I downloaded off of the web. It too shows a similar object. Since this picture is from the UK, I assume that this remnant is from a common type of fireworks.

I haven't touch this stuff since I was a kid. Can someone ID this remnant, and should it have gotten airborne?

Thanks,
David