Gaining acuity on crystal terminology in volcanic rocks

Given the prolific work on the petrography and mineral chemistry of volcanic rocks to understand magmatic processes for well over a century, it is surprising that there are no quantitatively rigorous size classifications or commonly accepted terminologies regarding the origin of such crystals. This causes some confusion when attempting to make meaningful statements about the origin of crystals in porphyritic volcanic rocks. Here, more rigorous size and genetic terminologies for the crystals in volcanic rocks are proposed (size, cf. Table 1: ultrananolite, nanolite, microlite, microcryst, mesocryst, macrocryst, megacryst; genesis, cf. Table 2: autocryst, antecryst, xenocryst). And some caveats are discussed. The genetic terminology may also be employed when interpreting crystal zoning patterns and can be applied to crystal fragments. Adoption of the proposed size classification scheme is expected to lead to quantitatively more precise descriptions of the dimensions of the crystal cargo in volcanic rocks in the literature. Adoption of the proposed genetic terminology is expected to lead to less ambiguous discussions of the genetic processes that operate in magmatic systems in the lead-up to volcanic eruptions.