- © 2017 by the Mineralogical Society of America
Crystals within volcanic rocks contain records of the changing chemical and thermal conditions within the magma reservoirs in which they resided before eruption. Observations from these crystal records place fundamental constraints on the processes operating within the reservoirs. Data from volcanic crystals are in accord with recent conceptual models of magma reservoirs being composed dominantly of crystal mushes, with small volumes and/or small fractions of melt present. The implication is that magma reservoirs have differing modes of behavior: magmas are stored over the long term in largely crystalline, quiescent, conditions, punctuated by brief episodes of intense activity during the decades to centuries immediately prior to an eruption.