Oxide reliably breaking down (8)

I believe the answer is:

beryllia

I'm a little stuck... Click here to teach me more about this clue!

'oxide' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.

'reliably breaking down' is the wordplay.
'breaking down' indicates anagramming the letters.
'reliably' with letters rearranged gives 'BERYLLIA'.

Can you help me to learn more?

Want a hint initially instead of a full solution? Install my app