UPDATE: Wishstone Rich in Phosphorus
And Titanium, relative to the average composition found so far.
Unusually Rich in Phosophorus
The graph in figure 1 compares the elemental makeup of a rock dubbed "Wishstone" with the average composition of rocks that Spirit examined on the western spur of the "Columbia Hills." Wishstone lies farther into the hills than that spur. It is richer in phosphorus than any other Mars rock ever examined. Scientists plan to examine other rocks near Wishstone to help explain the significance of the high phosphorus concentration. The vertical scale is the ratio of the concentration of an element in the hills rocks to the concentration of the same element in a typical volcanic rock from the plains that Spirit crossed to reach the hills
source
Well, the titanium works for my speculative sphene (CaTiO(SiO4), the Phosphorus brings the Apatite group minerals Nick pointed out into play (Pb5(VO4,PO4,AsO4)3Cl. Apatite is included in the mineral class: Phosphates, Arsenates, and Vanadates; which have some very interesting chemistries. Lots of various elemental substitutions within the crystal lattice.
Pyroxenes and amphiboles can contain Titanium.
Might this be a syenite after all? Someting fairly felsic, carbonatite? Now I'm really arm waving.
Of course, there are phosphates associated with the Evaporative Sequence!
Must do some thinking and reviewing.