Apparatus for the micronisation of a powdered material or product, or in general a material containing particles, comprising: - a container or receptacle, containing a reserve of the powdered material or product to be micronised; - a micronising mill specifically of the spiral jet-mill type with high-energy jets of a gaseous fluid, for example air, in which micronising spiral jet-mill the powdered material or product is micronised, said micronising spiral jet-mill in turn comprising an annular outer pressure chamber and a circular inner micronisation chamber, separated from one another by an annular intermediate wall which is provided with a plurality of channels or through holes, suitably inclined relatively to the radius of the micronisation chamber, which place the two chambers (12a, 12b) in communication, and - a feeding system for feeding the powdered material or product from the container to the spiral jet-mill, where it is micronised, characterised in that said feeding system comprises a volumetric microdispenser device designed to dispense and feed volumetrically the powdered material or product in a dense state to said spiral jet-mill, wherein said volumetric microdispenser device is directly connected via an outlet transport line, for transporting the powdered material from the microdispenser device to the spiral jet-mill, to said inner micronisation chamber of said spiral jet-mill and comprises one or more dispensing units associated with a suction line in which vacuum is created and a pressure line in which pressure is generated, wherein a plurality of control valves (26, 27) are fitted to place each dispensing unit selectively in communication with the suction line and the pressure line respectively, and wherein a plurality of control valves (28, 29) are fitted to place each dispensing unit selectively in communication with an inlet line, for transporting powdered material from said container to said microdispenser device, and the outlet line respectively, whereby said volumetric microdispenser device is designed to feed the powdered material directly to said inner micronisation chamber, where the powdered material is micronised, and the amount or quantity of the powdered material or product that is dispensed and fed to said spiral jet-mill in order to be micronised is determined in a precise way and is constantly controlled over time, - a container or receptacle, containing a reserve of the powdered material or product to be micronised; - a micronising mill specifically of the spiral jet-mill type with high-energy jets of a gaseous fluid, for example air, in which micronising spiral jet-mill the powdered material or product is micronised, said micronising spiral jet-mill in turn comprising an annular outer pressure chamber and a circular inner micronisation chamber, separated from one another by an annular intermediate wall which is provided with a plurality of channels or through holes, suitably inclined relatively to the radius of the micronisation chamber, which place the two chambers (12a, 12b) in communication, and - a feeding system for feeding the powdered material or product from the container to the spiral jet-mill, where it is micronised,