This sequence of linear volcanic activity is referred to as the Taranaki Volcanic Succession. Except for the Paritutu centre, all of the cones are composed of andesite (a fine-grained rock of intermediate composition between basalt and rhyolite). In hand specimens, the Egmont andesite is a light or dark greyish rock with numerous white speckles (feldspar crystals) and dark green squat (augite) or black needle-shaped (hornblende) crystals within a glassy matrix. In the central parts of Pouakai and Kaitake coarser grained rocks (diorites) which cooled inside the volcano but which are now exposed by erosion of overlying materials, show a network of larger black and white crystals with very little matrix. Other materials derived from the volcanoes include large thicknesses of air-fall deposits or tephra. Tephra consists of all the materials aerially ejected from a volcano and may be subdivided into ash (if less than 2 mm particle size), lapilli (particle size between 2 and 64 mm) and blocks (greater than 64 mm).