Stone entrance? (5)
I believe the answer is:
agate
'stone' is the definition.
(I know that agate is a type of calcedony)
'entrance?' is the wordplay.
I cannot really understand how this works, but
'entrance?' could be 'gate' (type of entrance) and 'gate' is found in the answer.
A single letter 'a' remains which might be clued in a way I don't see.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for agate that I've seen before include "Quartz with bands of colour, used in jewellery" , "Type of quartz" , "rock with bands" , "Quartz variety" , "Semi-transparent stone" .)