"solid cornerstone" is correct and usable in written English.
You might use it to refer to something that provides a reliable foundation on which to build. For example, you could say "Education is a solid cornerstone - providing children with the foundation they need to become successful adults."
A $100-million endowment could give MOCA a solid financial cornerstone at last, but it's unclear whether the results so far will provide much help with the immediate operating needs that would concern a new museum director.
I would focus on the next two to three years as being the financial cornerstone and allow other plans to develop once this solid base has been established".
Building on her long-nurtured image as frugal, commonsense homemaker, the chancellor painted the 127-page election manifesto as a solid foundation for the country's future — forgoing tax increases, but still chipping away at Germany's outstanding debts, and ensuring that budget consolidation would remain a cornerstone of a "moderate and balanced" program.
"The NSF's cornerstone remains solid, but its boarded up windows are what need repair".
The calcineurin inhibitor cyclosporin A (CsA) is a potent immunosuppressive agent that has formed the pharmacologic cornerstone of solid organ transplantation.
Basic science research has always been the cornerstone of a solid academic career, even for surgeons.
Workout partners usually chat during the routine, and communication is the cornerstone of any solid relationship.
The present study deals with the addition of porous membrane as modifier for the crystal structure of solid hydrocarbons, which will be the cornerstone in rearrangement and reformulation of new hard crystals in deoiling process.
Tacrolimus is a cornerstone of immunosuppressive treatment after solid organ transplantation.
