One analysis point from the light pink area of a watermellon tourmaline from this locality is rossmanite. The dark pink core is liddicoatite and the rim is green liddicoatite.
Tanzanian watermelon tourmaline from
Giller (2003) p130.
Composition:
([]0.374Na0.268Ca0.352K0.006) [Al1.585Li1.396Mn0.018] Al6.00 BO3 [Si5.833Al0.167 [(OH)3.624F0.376]
Reference:
Giller BS (2003) An overview of tourmaline mineralogy from gem tourmaline producing pegmatite districts in Africa. Master of Science Thesis, University of New Orleans, LA. http://etd-db.uno.edu/theses/submitted/etd-05062003-151714/unrestricted/2003_05_ms_giller_brian.pdf