The invention relates to the selection of a natural calcium carbonate
crushed to a high degree of fineness, possibly treated with one or more
fatty acids or one or more of their salts or mixtures thereof, and its
use as a rheology regulator for polymeric compositions.The specific
surface area is 14 to 30 m.sup.2/g measured according to the BET method
to ISO 4652, and the oil absorption is greater than 16 measured according
to ISO 787-V (Rub-out method).The conditions of mixing of the
constituents and manufacture are improved, as well as the properties of
the final product.