The phrase "a marginal part of" is correct and usable in written English.
It can be used to describe something that is not central or significant within a larger context or framework.
Example: "The findings of the study were interesting, but they represented only a marginal part of the overall research landscape."
Alternatives: "a minor aspect of" or "a peripheral element of".
This is not a marginal part of our entertainment.
Yet the voluntary and community sector is no longer a marginal part of the economy.
And MTV Networks itself, like most cable channels, was considered a marginal part of the television business, a flea on the back of the broadcast network elephants.
Once considered a marginal part of the business, E.D.M. now draws more than 100,000 fans to festivals and is lucrative enough to attract Wall Street investment scouts.
Long considered a marginal part of the music business that subsisted in clubs and semi-legal warehouse raves, dance has now moved squarely into the mainstream, with a growing circuit of festivals and profit margins that are attracting Wall Street.
3. Why aren't bankers and traders required to have more skin in the game — that is, more of their own salary at risk — and not just a marginal part of one year's bonus?
Pew notes that e-book borrowers are on the rise, but represent a very marginal part of the population, up to 5% from 3% the year before.
Futures research forms a very marginal part of the activities of universities and large research companies throughout Europe [1, p 25].
Even if we assume (as we might, sounds like the sort of thing that might be true) that US coins must be made of US produced metal this is still a very marginal part of the total market.
A possible explanation is the contrasting relative abundance of the two species at Bejan: Q. petraea is very common in the study area while Q. robur is frequent only in a small marginal part of the reserve.
To some visitors, "Bataille Monument" was an ugly intrusion into an already marginal part of the city; to others, like the New York Times critic Michael Kimmelman, the project was among the best offerings in an otherwise "claustrophobic" show.
