Angular, glassy particles, less than 2 mm in size, formed either by the explosive magmatic fragmentation of pumice vesicle walls, or by the chilling and brittle fragmentation of magma when it comes into contact with groundwater or surface water. Magmatically formed shards commonly have ‘Y’ or cuspate shapes and may deform plastically and weld together if they are hot enough when deposited and the overburden load is sufficient. Shards formed by hydrovolcanic processes have a variety of shapes, ranging from those with curviplanar surfaces and low vesicularity to those with smooth, fluid-form surfaces and moderate vesicularity.