PURPOSE: To enhance the grinding efficiency of heavy calcium carbonate within the same grinding time as compared with the grinding of a single component, by mixing heavy calcium carbonate and talc to prepare a slurry which is, in turn, subjected to wet grinding.

CONSTITUTION: Heavy calcium carbonate is pref. mixed with 3W70wt% of talc to prepare a slurry mixture of which the solid concn. is pref. 50W78wt%. Wet grinding is applied to said slurry mixture. At the time of the mixing preparation of heavy calcium carbonate and talc, a dispersant such as sodium polyacrylate or sodium ligninsulfonate can be added and the addition amount thereof may be 1% or less. As the apparatus for wet grinding of the aforementioned slurry mixture, a sand grinder, a Dynomill or a supermill can be used.