The phrase "also a cornerstone of" is correct and usable in written English.
It can be used to indicate that something is an essential or foundational element of a larger concept or system.
Example: "Education is also a cornerstone of a successful society, providing individuals with the skills they need to thrive."
Alternatives: "also a fundamental part of" or "also a key element of".
They are also a cornerstone of the Trump Organization.
The drug is also a cornerstone of antiretroviral AIDS treatment in poor countries.
That means not only is failure critical to success but it's also a cornerstone of happiness.
Teams represent not only a slice of a metropolitan economy, but also a cornerstone of its collective identity.
Residential life is also a cornerstone of the learning experience; students and teachers live, work, and play together.
The core principle of Warren's work is also a cornerstone of economic theory: well-informed consumers make for vigorous competition and efficient markets.
It has also threatened a cornerstone of President Álvaro Uribe's strategy to pacify the country.
Mr. Siegert photographs them at work on the building sites instead of sitting them down in front of the cameras to talk about themselves; he is savvy enough to use the documentary form to reveal his characters, while showing that people in action can also be a cornerstone of drama.
In addition, it will also become a cornerstone of Firefox OS, Mozilla's budding operating system for mobile devices.
It would also become a cornerstone of Aretha Franklin's return to gospel music in a live recording at New Temple Missionary Baptist Church in Watts, Los Angeles in January 1972.
And some of the work that the DNI has been running and funding also formed a cornerstone of Google's recently announced AMP (accelerated mobile pages) project, tech that Google has developed to produce faster-loading sites for smaller screens.
