Robert Haar said something like:
Of course, I believe that quartz changes the situation a little.
From:
Potassium Feldspar: hardness of 5 1/2 - 6 1/2, pink to light gray, two good cleavages at right angles, opaque, rectangular minerals with good cleavage.
Plagioclase: hardness of 5 1/2 - 6 1/2, gray, two good cleavages at right angles, striations on one cleavage, opaque, rectangular minerals with good cleavage and striations.
Clay: aphanitic, soft, usually gray, but can be red or green, looks muddy.
Calcite: hardness of 3, fizzes in acid.
Dolomite: hardness of 3, fizzes in acid when it is powdered. To powder the mineral, scratch it with a knife, steel nail, or other metal object.
Halite: hardness of 2, tastes salty.
Gypsum: hardness of 2, does not taste salty.