I have 3 bits of similar rock from Wyre Forest in West Midlands. I know there was a lot of charcoal making here in Victorian period, so I don't even know if they're natural like chert, or slag from the industry. Anyone any thoughts? They come in blue and green, you can just see the blue on one piece. They are a hard waxy lustre. I haven't done a streak test because i can't find anything suitable to use.