Take an ordinary microscope and look for the garnets in the slurry.

Make some slurry, put it on a slide, use 400x magnification. Look here for what you need to see: http://www.belgischerbrocken.com/

Click info's and then: Mikroskopisch Ergebnis etc not the first picture but the third because the crystals are red. Unfortuantely I never managed to upload pictures for SRP.