an aggregate of {TAIL ~ granular crystals} precipitated on said columnar crystals that has {HEAD ~ a hardness} lower than that of the columnar crystals 
an aggregate of { TAIL ~ granular crystals } precipitated on said columnar crystals that has { HEAD ~ a hardness } lower than that of the columnar crystals
OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH