A lot of sediment, one about to reveal constituent of sand (6)
I believe the answer is:
silica
'constituent of sand' is the definition.
(I've seen this before)
'a lot of sediment one about to' is the wordplay.
'a lot of' means to remove the last letter (a lot of the word but not all of it).
'sediment' becomes 'silt' (I've seen this before).
'one about to' becomes 'ica' (I am not sure about this - if you are sure you should believe this answer much more).
'silt' with its final letter taken away is 'sil'.
'sil'+'ica'='SILICA'
'reveal' is the link.
Can you help me to learn more?
(Other definitions for silica that I've seen before include "Compound in quartz" , "Oxide occurring as quartz and used in making glass" , "Glassy substance in quartz and sand" , "Constituent of sandstone and quartz" , "Quartz used in the manufacture of glass" .)