Task: Class Definition Understanding (ontology: Earth_Environment/SWEET)

Which of the following definitions best describes 'phenocryst'?

A. Constituent occurs as crystals formed by metamorphic crystallization, set in a finer-grained groundmass.
B. A migratory wavelike disturbance of the tropical easterlies.
C. A the concept is a relatively large and usually conspicuous crystal distinctly larger than the grains of the rock groundmass of a porphyritic igneous rock. Phenocrysts often have euhedral forms either due to early growth within a magma or by post-emplacement recrystallization. [Wikipedia]
D. Relict crystal in metamorphic rock, in groundmass of relatively finer-grained material. Connotes that groundmass is result of tectonic reduction in grain size.

Answer: A the concept is a relatively large and usually conspicuous crystal distinctly larger than the grains of the rock groundmass of a porphyritic igneous rock. Phenocrysts often have euhedral forms either due to early growth within a magma or by post-emplacement recrystallization. [Wikipedia]