Latvian clays of three geological ages – Devonian, Jurassic and Quaternary from four deposits are investigated with purpose to produce expanded clay granules. Saw dust in amount of 2wt% is added and granules from plastic ceramic body are formed. Thermal treatment in two different ways is carried out. The first way is one stage: the firing from 20˚C at temperature rising rate 1000˚C/h. The second way is carried out in two stages: the input of granules heated up to 700˚C in the furnace with max temperature. The holding time at the final firing temperature 1150˚C by both firing ways is 10 min. Granules of expanded clay with various bulk densities and various coefficient of volume increase are obtained. Granules produced from Quaternary clays of deposits Apriki and Laza by two stage process have the lowest bulk density and highest coefficient of volume increase. Coefficient of volume increase varies in the range 3.9 – 5.8. The production of expanded clay granules from these clays is possible also without combustible additives. Chemical processes in clays occurring as the result of thermal treatment are investigated using differential thermal analyses. Determination of crystalline phases in the clays and the obtained materials is carried out using X-ray phase analysis. The pyroplastic state of material during expanding determines the properties obtained by materials. Pyroplastic state in case of granules from Quaternary clays requires the presence of potassium and calcium feldspars which crystallise during cooling of the expanded materials.