Quartz, potassium feldspar and plagioclase constituting the light non-magnetic rock component of most crystalline rocks are separated using flotation and fractionated density separation. For the feldspar flotation a medium containing 0.4 g of the ANP-14 collector and 3 ml of 40% hydrofluoric acid per 1000 ml of distilled water is employed. Quartz admixture in the feldspar fraction is determined with the aid of an x-ray diffractometer. Line 101 of quartz and 002 lines of potassium feldspar and plagioclase scanned between angles 2 0 24.5 degrees and 28.5 degrees served for determination. The feldspar fraction is further separated by fractionated centrifuging in a mixture of bromoform and dioxane. A simple device is described for easy removal of the light fraction from a normal centrifuge tube after centrifuging. It consists of a drawing pin cut at one side and shaped to form a spiral surface. The point of the pin is molten into one end of a thin glass stick. When rotated and pushed slowly into the layer of the light fraction the device operates as a soil-borer without perturbing the layer. Afterwards, practically all the light fraction can be removed by carefully pulling the stick. The remaining small amount of the light fraction can be easily poured out together with part of the liquid without mixing it with the heavy fraction.