Increase gold and gem layout on book (7)
I believe the answer is:
augment
'increase' is the definition.
(I know that augment is a kind of increase)
'gold and gem layout on book' is the wordplay.
'gold' becomes 'Au' (Au is the chemical symbol for gold).
'and' is a charade indicator (letters next to each other).
'layout' indicates an anagram (an alternative layout of the letters).
'on' means one lot of letters go next to another.
'book' becomes 'nt' (New Testament).
'gem' anagrammed gives 'gme'.
'au'+'gme'+'nt'='AUGMENT'
(Other definitions for augment that I've seen before include "Increase number of" , "get longer" , "Enlarge or increase" , "boost" , "Supplement" .)