NOVELTY - An aluminum-containing starting silicon material melt (2) is solidified by cooling in mold under a unidirectional temperature gradient condition to give directionally-solidified silicon (4) containing purified silicon region having aluminum concentration not higher than the predetermined maximum level of aluminum concentration (C10max (ppm)) and crude silicon region having aluminum concentration (C) higher than (C10max (ppm)). The crude silicon region is separated from obtained directionally-solidified silicon to give purified silicon.    USE - Production of purified silicon used for solar cells.    ADVANTAGE - The method effectively provides silicon with high purity.    DETAILED DESCRIPTION - An aluminum-containing starting silicon material melt is solidified by cooling in mold under a unidirectional temperature gradient condition to give directionally-solidified silicon containing purified silicon region having aluminum concentration (C (ppm)) not higher than the predetermined maximum level of aluminum concentration (C10max (ppm)) and crude silicon region having aluminum concentration (C) higher than (C10max (ppm)). The crude silicon region is separated from obtained directionally-solidified silicon to give purified silicon having aluminum concentration (C) not higher than (C10max (ppm)).During separating crude silicon region, the directionally-solidified silicon is cut at portion corresponding to standard solidification fraction (f0) obtained from (C10max) and temperature gradient (T) and solidification speed (R (mm/min)) in cooling the starting silicon material melt and satisfy formulae (1 and 2). The standard solidification fraction (f0) indicates ratio of purified silicon region having aluminum concentration not higher than (C10max), to whole of the directionally-solidified silicon. fo is 0-1. The starting silicon melt satisfy formulae: k=(K1x Ln(R)+K2)x (K3x exp(K1x Rx (K5x C2+K6)))x (K7x T+K8)-K9 (1) and C10max=kx C2x (1-f0)(power)k'-1 (2). Where, K1 is 1.1x 10-3 greater than or equal to 0.1x 10-3, K2 is 4.2x 10-3 greater than or equal to 0.1x 10-3. K3 is 1.2 greater than or equal to 0.1, K4 is 2.2 greater than or equal to 0.1, K5 is (-)1x 10-3 greater than or equal to 0.1x 10-3, K6 is 1 greater than or equal to 0.1, K7 is -0.4 greater than or equal to 0.1, K8 is 1.36 greater than or equal to 0.01, K9 is 2x 10-4 greater than or equal to 1x 10-4, R is solidification speed and T is temperature gradient. The predetermined maximum level of aluminum concentration is 1/1000-3/100 times aluminum concentration of starting silicon material melt.    DESCRIPTION OF DRAWING(S) - The drawing shows cross-sectional view of process of obtaining directionally-solidified silicon.    Starting silicon material melt (2)    Directionally solidified silicon (4)    Crude silicon (5)    Heater (6)    Furnace (7)