One of my trades reckons it's not - although he claimed it's "asbestolite" because it contains shiny crystals, which he thinks is a safe replacement for asbestos. Googling, though, asbestolite appears to be just a brand name for deadly old proper asbestos. I'm pretty sure I've not been exposed as it was removed by the guy who thinks it's not asbestos and left in the back yard.
http://tinypic.com/view.php?pic=zj8pz5&s=9
http://tinypic.com/view.php?pic=zj8pz5&s=9