A ballistic mass of lava, usually greater than 64 mm in size, ejected from a source vent. The exterior of the lava rapidly chills to form a fine-grained, glassy crust, which is then cracked open by continued vesiculation (see vesicle) and the expansion of the hot lava interior. The cracking of the crust resembles that sometimes seen on loaves of bread baked in the traditional manner.