Ilmenite is an economically important and interesting mineral. Ilmenite forms as a primary mineral in mafic igneous rocks and is concentrated into layers by a process called "magmatic segregation". It crystallizes out of a magma relatively early before most of the other minerals. As a result, the heavier crystals of ilmenite fall to the bottom of the magma chamber and collect in layers. It is these layers that constitute a rich ore body for titanium miners. Ilmenite also occurs in pegmatites and some metamorphic rocks as well as in the sedimentary rocks that are formed from the weathering and erosion of them. Ilmenite is a metallic to submetallic mineral that is generally iron black. At times it can form brightly lustered intricately faceted crystals or radial clusters arranged in a rosette fashion. Platy hexagonal crystals with rhombohedral faces on the edges can appear very similar to hematite's tabular habits. However hematite has a distinctly different streak. Magnetite is also similar and easily confused with ilmenite, but ilmenite has a different crystal form and is not as strongly magnetic.