Pyroclastic rocks form when explosive stratovolcanoes erupt.
They are extrusive
igneous rocks with fragmental texture.
They form in the air,
when volcanic ash, debris and
other volcanic material is thrown into
They can also consist of pieces of other rocks, glass and
mineral crystals, or be a mixture of them all.
Tuff by Ian Geoffrey Stimpson via Flickr.com
The fragments have first solidified, and then, later cemented or packed
together. One very good example is tuff.