Chalk, limestone and marble extenders of various origins were studied for particle size distribution, phase compn. and rheol. of their aq. suspensions. Size median (1.08 to 24.36,mu m), flatness and packing coeffs. of the extender particles (1.010 to 2.450 and 0.667 to 0.0.803, resp.), plastic viscosity and flow limit of the suspensions (0.015 to 9.612 Pa.s and 0.00 to 140.76 Pa, resp.) as well as whiteness coeff. of the coatings (50.35 to 90.69) were detd. The rheol. properties of the extenders were detd. both in aq. extender pastes (47.2% by vol.) and in model suspensions consisting of the extender, titanium white pigment and styrene-acrylic dispersion. The viscosity and flow limit of the suspensions were highly dependent upon the extender particle size and cryst. structure as well as kind of impurities in the extender deposit (mainly p-quartz and mica). The expts. on the ternary extender mixts. were statistically planned and underwent to the Simplex analysis. The optimum compns. of the suspensions were also established in respect to their rheol. and optical properties. The best compns. were achieved at maximum packing of the pigment and extender particles.