"such a gem" is a correct and usable phrase in written English.
You can use it to describe something that is lovely or impressive. For example, "That sunset was such a gem!".
That's why the Shanty is already such a gem.
If ever there was such a gem then it was John Cage.
To pen such a gem of a phrase is every young journalist's dream.
Most cooks love it and that's because it is such a gem.
"I am really tickled that I lucked into such a gem," he said.
"Rockefeller Center is such a gem and has such historical significance that we will look at this very, very carefully".
Every club craves unearthing such a precious gem as Hernandez, who scored 20 goals in a memorable debut season at Old Trafford.
I think I feel wrong about it because it is such a fucking gem why wouldn't anyone publish it?
The piece offers four "scenes," meant to demonstrate the difficulties of being with such a precious gem of a woman.
"What makes San Francisco such a rich gem is not only its beauty but the way in which people from all over the world come together here.
