Volcanic ejecta. Artwork of different forms of pyroclastic material, or tephra, ejected by an erupting volcano. Volcanic ash (top) consists mainly of very fine fragments of glass mixed with rock and crystal. Individual fragments are smaller than 2 millimetres in diameter. Lapilli (little stones, middle) are lava and rock fragments measuring between 2 and 64 millimetres in diameter. Volcanic bombs (bottom) are blocks of semi-molten lava. They often take on streamlined shapes as they are cooled by flying through the air.