Study the island of sand and cement (8)
I believe the answer is:
concrete
'sand and cement' is the definition.
(I've seen this before)
'study the island' is the wordplay.
'study' becomes 'con' (con can informally mean to study).
'the island' becomes 'crete' (Greek island).
'con'+'crete'='CONCRETE'
'of' acts as a link.
(Other definitions for concrete that I've seen before include "Solid, real" , "Actual - stuff made with cement" , "Real; building material" , "Real, not abstract" , "Solid like building material" .)