Quaternary (Q-clay) clayey deposits are one of the dominating parts of mineral raw materials of the sedimentary cover at present area of Latvia. These clays can be characterised by illite content up to 75-80 %. Two ways for use of illite clays were studied: conventional and geopolymers method. Purpose of the second mentioned method was showing the influence of alkali (KOH) on the transformation of Q-clay/illite structure. Obtained products were investigated by IR–spectroscopy, DTA and XRD, pore size distribution was determined as well. Some ceramic properties and compressive strength were determined and compared. IR-spectrum showed the effect of alkali on the transformation of Q-clay/illite structure in three main absorption bands: 3620-3415 cm-1 which is related to the vibrational modes of adsorbed water between SiO4 and AlO6 layers; new stronger absorption bands at 1635 cm-1 and 1435 cm-1 indicate on the appearance of vibrations in Q-KOH and are related to the K-O-Si bonds; the most essential changes are vibrations at 779 and 684 cm-1 showing on the disconnection of Si-O-Al bonds and vibrations among SiO4 and AlO6 layers. X-ray diffraction spectra of Q-clay and Q-clay/KOH shows the changes in the intensity of illite peaks. Investigations of the bulk density in dependence on temperature showed the relatively remarkable decrease of bulk density for Q-clay while - the small for Q-clay/KOH. Mentioned values correlate with the compressive strength of Q-clay and Q-KOH products.