Gypsum and basalt are rocky (9)
I believe the answer is:
alabaster
'gypsum' is the definition.
(I've seen this before)
'basalt are rocky' is the wordplay.
'rocky' indicates anagramming the letters (letters rocked or thrown around).
'basalt'+'are'='basaltare'
'basaltare' with letters rearranged gives 'ALABASTER'.
'and' acts as a link.
(Other definitions for alabaster that I've seen before include "White translucent form of gypsum used for statues, vases etc" , "White or translucent mineral" , "Altar base (anagr.)" , "Arabs tale (anag.)" , "medium of sculpture" .)