Ruins lab coat, spilling a chemical element (6)
I believe the answer is:
cobalt
'chemical element' is the definition.
(cobalt is a kind of chemical element)
'ruins lab coat spilling a' is the wordplay.
'ruins' is an anagram indicator.
'spilling' indicates named letters should be taken away (deleted letters spill out).
'lab'+'coat'='labcoat'
'labcoat' with 'a' taken out is 'lbcoat'.
'lbcoat' is an anagram of 'COBALT'.
(Other definitions for cobalt that I've seen before include "Metallic element, Co" , "Metal element" , "Deep blue pigment" , "Element 27; a deep blue" , "Ferromagnetic metal - shade of blue" .)