These and other minerals, including minerals of tin and tungsten, monazite, tourmaline, rutile, and various precious stones, are characteristically developed in pegmatites, which are known to be igneous rocks, crystallized in the later stages of igneous intrusion.
"The Economic Aspect of Geology"
C. K. Leith
rutile and ilmenite both have high specific gravity and are little affected by weathering.
"The Economic Aspect of Geology"
C. K. Leith
The diamonds are found in the sands and gravels of river-beds, associated with alluvial gold, specular iron ore, rutile, anatase, topaz, and tourmaline.
"The-Romance-of-Industry-and-Invention"
Cochrane, Robert