This immediately made me wonder what "cacoxenite" was made of. Being a scientist type, I wasn't satisfied to know just that it was a "rare iron phosphate mineral". I had to know more.
So I found more. Here's the total story on cacoxenite:
Fe24 (AlO6) (PO4)17 (OH)12 - 75H2O is the mineral formula.
Site:
Cacoxenite: Hydrated Iron Aluminum Phosphate Oxide Hydroxide
"Cacoxenite on its own is appreciated as a scarce phosphate mineral and is known from classic phosphate localities. It is often associated with other attractive and rare phosphates and can therefore represent some very nice mineral specimens. These specimens can be quite popular and attractive with a silky luster and a typical yellow-brown color."