I guess I had do some mop up on my study of mineralogy and blogging thereof. The next consideration is phosphates, arsenates, and vanadates. Many of these are useful as gemstones due to their attractive qualities. The phosphate that comes to mind is turquoise. It is found in igneous rocks and some pegmatities. Its color and veining makes it very popular as a gemstone.
Lazulite is a blue magnesium iron-aluminum phosphate. It could easily be confused with lazurite or lapis lazuli (a rock not a mineral). Lazulite crystals are popular as gemstones due to their unusual blue color.