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