Alum shale, page-56

Most deposits of this type also contain other commodi- ties, notably iron, titanium and in some cases phosphorus, and mineralogy is thus critically important in all cases. The principal oxide minerals are generally magnetite (Fe3O4) and ilmenite (FeTiO3). Vanadium is generally concentrated in magnetite, whereas titanium is in ilmenite. Apatite is the most common P-bearing host mineral, and apatite-rich rocks may themselves be important as phosphorus sources. How- ever, these minerals may be intergrown finely, such that they can be very difficult to separate physically. In some cases, titanomagnetite (Fe2TiO4) may still be present, and can also host vanadium, but it more commonly exsolves into mag- netite and ilmenite (Gross, 1995).

The section above is on page 4 of the following document 

https://www.nr.gov.nl.ca/nr/mines/geoscience/publications/currentresearch/2013/Kerr-Walsh_2013.pdf