1. The method of photometric sorting non-uniformly colored coarse mineral articles such as lumps of limestone and dolomite of changing form which differ from each other both in color and in size which comprises: illuminating each said article to cause light to be reflected therefrom, filtering the reflected light to extract at least two frequencies therefrom whereby the intensities of at least two discrete wave length ranges of light reflected from each said article become measured several times, separately detecting the extracted frequencies and developing electrical signals in conformity with the intensity of the respective extracted frequency, forming a quotient from a sum of the individual signals pertaining to each article, and developing a further output signal to control sorting out of the coarse articles in cOnformity with the said quotient only when the sum of the individual signals exceeds a preset number of sequential impulses.

5. An apparatus for sorting coarse articles, such as lumps of limestone and dolomite, which differ from each other both in color and size which comprises: first means for supporting the article, second means for illuminating said articles, a pair of identical photosensitive elements, a filter between each said element and said illuminated article adapted to pass a respective frequency of the light reflected from said illuminated article, each said photosensitive element being adapted to develop a signal in conformity with the intensity of the light falling thereon from the respective filter, and circuit means supplied by said signals and operable to develop a further sorting signal in conformity with the quotient of the said signals supplied thereto.