I think that they are similar - around 7 on Mohs scale.
Whilst you can probably find everything you need on the internet about grinding, polishing, figuring and testing, there is a wonderful series of books:
http://www.amazon.com/Amateur-Telesc.../dp/0943396484
in three volumes. The originals were published in the 1930's when they knew how to do this stuff! They are a joy to read...
(I know that Sirius Optics have a set in stock - I saw them there last weekend!)