Boundaries between phoscorite types, carbonatite and host rocks in terms of bulk-rock chemistry. X-axis is rock name (letters C, M, A, F are mineral indexes in phoscorite name: calcite, magnetite, apatite and forsterite, correspondingly, classification is shown in Fig. 2). Y-axis is chemical composition of rocks; bold numbers are values for logical evaluation of a rock type (Fig. 4).