Abstract: The invention relates to a method for improving vermiculite's intake of ammonium, in which method heating of the crude vermiculite is conducted to a temperature where vermiculite's third dehydration step takes place, the temperature being lower than the temperature where vermiculite's fourth dehydration/dehydroxylation step takes place. The invention relates also to use of the obtained vermiculite and to an absorption material, comprising vermiculite material and additives, where at least 50% of the vermiculite material comprises vermiculite, which has undergone the third dehydration step but not the fourth dehydration/dehydroxylation step. The invention relates also to use of thermally treated and ammonium doped vermiculite as fertilizer/soil conditioner.