In areas where volcanic activity stopped after the first eruption all that may be present is a mixture of volcanic and non-volcanic rocks. If volcanism continued, successive layers of volcanic material, representing each eruptive phase, would be piled upon the initial non-volcanic fragments. Lapilli are commonly associated with bombs and blocks in agglomerates, as well as tuff. Basaltic lapilli which is dark and vesicular are also called scoria or cinders. Acid volcanoes produce highly vesicular lapilli size fragments called pumice.
Pumice has such a low density it can often float on water.
If the gas bubbles continue to expand it can shatter lapilli into pieces of vesicle walls. They are common in fine ash and tuff. Lapilli are frequently present in graded beds consisting of bombs and lapilli at the base and ash on the top. These occur due to the falling out of the bombs, followed by lapilli and finally ash, from the air. If strong winds were present at the time of deposition, aeolian crossbedding may occur.