A possible option is to invite him to have a 'great debate' with you on this forum.
A 'great debate' is a slightly moderated debate where you choose who can join in (rather than a free-for-all).
You could then choose one of the geologists on this forum to help with the geology questions.
Just a thought...
If I were you
And I wish that I were you
All the things I'd do
To make myself turn blue