Piece of stone from his laboratory (4)
I believe the answer is:
slab
'piece of stone' is the definition.
'slab' can be an answer for 'piece' (I have seen 'Piece of paving' mean 'slab' so perhaps 'piece' could also mean 'slab'). I'm unsure of the 'of stone' bit.
'from his laboratory' is the wordplay.
'from' indicates the answer is hidden within the clue.
'SLAB' is hidden within 'his laboratory'.
Can you help me to learn more?
(Other definitions for slab that I've seen before include "Paving stone" , "Large piece (of chocolate, stone, etc)" , "Hunk" , "Large block of stone or concrete" , "24 tinnies [STRINE] < in a wooden hut [STRINE]" .)