Perlite
http://t3.gstatic.com/images?q=tbn:ANd9GcRLBz9VlvwPlo6MAxoAmwru7uLCM841_-jJPvhJ4VT7gMWSFOX2VQ
Rock wool
http://t0.gstatic.com/images?q=tbn:ANd9GcTqN-oeXyhfJHWJ6t_SR-F4mK2h7sffYhz9FWniWD3Vo4JEo2rA
http://t1.gstatic.com/images?q=tbn:ANd9GcQ8Sri8h0i_Xb9ZoNfFABUeSeNDXdLSoMQAU4wLlUIJNguzWJa8