The effect of varying R=[CaO]/([CaO]+[Na2O]) ratio on the crystallization of a rare earth-rich aluminoborosilicate glass (16 wt% RE2O3, RE=Nd or La) is investigated. The crystallization of a silicate apatite with Ca2+xRE8-x(SiO4)(6)O2-0.5x composition (x approximate to 0.4-0.7), is responsible for a drop of the rare earth solubility in the melt. When successive nucleation and growth stages are performed, crystallization processes change across the glass series as a consequence of glass-in-glass phase separation. An exotic phase of composition close to Ca10Nd7Si20.75O62 grows at the expense of silicate apatite.