Raw ash derived from the burning of lignite optionally modified by (i) removal of Fe compds. in the ferromagnetic separator, (ii) burning of coal in oven (800 degrees C, 6 h) was used to obtain geopolymers. Mixts. of aq. Na glass and NaOH were used in different proportion as activators. Modification (i) and use of an activator with dominant NaOH content significantly improved the compressive strength parameters of geopolymers.