Rocks are naturally occurring solids which are composed of minerals & have been used by humans since ages. From Stone Age, rocks are used for various purposes. Also, the metals and minerals found in rock play an important role in our life. Get to know all the Trondhjemite Uses. We have provided you with all information about Trondhjemite rock here. Trondhjemite is a leucocratic (light-colored) intrusive igneous rock. It is a variety of tonalite in which the plagioclase is mostly in the form of oligoclase. Trondhjemites are sometimes known as plagiogranites.. Trondhjemite is available in black, brown, light to dark grey, white colors. The streak of a rock is the color of powder produced when it is dragged across an unweathered surface. The streak of Trondhjemite is bluish black. Get to know more about Trondhjemite rock and characteristics of Trondhjemite rock in the next sections.