Volcanic ash is quite different from more familiar types of ash, such as that generated by burning paper or wood. Instead of being soft or fluffy, the pyroclastic material is hard and insoluble in water. Particles of volcanic ash may also be much smaller than other ashes, often exhibiting diameters less than a thousandth of an inch in size. The mineralogical composition of volcanic ash generally depends upon the type of volcano it originates from and whether or not the material it ejects is primarily acidic or basic in nature.