Trondhjemites are very common rocks, found all over the world. The classic locality is at Follstad (Støren), about 50 kilometers south of the city of Trondheim. This is a quarry where blocks of trondhjemite are taken for cutting and polishing large slabs, which are used for the walls and floors of special buildings. This rock is about 432 million years old.
There are also large bodies of trondhjemite within walking distance of the city center, but these have been strongly metamorphosed or altered and are now best called gneiss, and not trondhjemite. They are about 482 million years old.
A detailed study of the trondhjemite of Follstad was published by W.B. Size 1979: Petrology, geochemistry and genesis of the type area trondhjemite in the Trondheim Region, Central Norwegian Caledonides, Norges geologiske undersøkelse 351, pages 51-76.