Rock offering shade on beach (9)

I believe the answer is:

sandstone

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'rock' is the definition.
(sandstone is a kind of rock)

'shade on beach' is the wordplay.
'shade' becomes 'stone' (I can't explain this - if you can you should give a lot more credence to this answer).
'on' means one lot of letters go next to another.
'beach' becomes 'sand'.
'stone' put after 'sand' is 'SANDSTONE'.

'offering' acts as a link.

Can you help me to learn more?

(Other definitions for sandstone that I've seen before include "Type of sedimentary rock" , "Among the best of building materials" , "Rock containing quartz grains" , "Such building material" .)

I've seen this clue in The Telegraph.

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