In igneous petrology, a phenotype is an aphanitic igneous rock which is identified and classified according to the mineralogy of its phenocrysts, when it is impossible to determine the mineralogy of the groundmass.^[1] Because phenocrysts represent the earlier part of crystallisation, and a melt may have evolved somewhat in between stages of cooling, they cannot be used to accurately describe the rock's true mineralogy or chemistry, but do provide an approximate estimation. As a result of this potential for error, phenotypes are identified using the prefix pheno-.^[1]

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