Nickel

Nickel (similar to iron) is one of the most common elements available on earth and in space.
The usage of nickel in advanced atomically precise technology as structural building material has some issues though.

There seem to be very view nickel minerals with clear stoichiometry. One is the mineral:

• Bunsenite NiO [1] (Mohs hardness 5.5)

Can practically faultless mechanosynthesis suppress diffusion sufficiently?

(TODO: Investigate further to find the best nickel based abundant element gemstones.)