For example, goes over verse describing where crystals might be found (5)
I believe the answer is:
geode
'where crystals might be found' is the definition.
The definition suggests a singular noun which matches the answer.
'for example goes over verse' is the wordplay.
'for example' becomes 'e.g.' (short for 'exempli gratia', 'for example' in Latin).
'goes over' shows that the letters should be reversed in order.
'verse' becomes 'ode' (ode is a type of poem or verse).
'eg' back-to-front is 'ge'.
'ge'+'ode'='GEODE'
'describing' is the link.
Can you help me to learn more?
(Other definitions for geode that I've seen before include "Crystal-lined cavity in rock" , "Druse" , "Small rock cavity" .)