Silt grains are rock particles even smaller than sand (less than 0.06 mm or 0.002 inch wide), so water and wind can transport them farther than sand grains. When the water in a pond appears brown and difficult to see through, it may be carrying large amounts of silt, which is slow to settle to the bottom. Quartz and feldspar, both silicates, are the most common minerals in silt. Once silt hardens into rock, scientists usually cannot see the individual grains without the aid of a microscope. Mud is a mixture of water, silt, soil, and clay (the tiniest of all rock particles). Mudstone, the sedimentary rock made of mud, often breaks into random blocks, and it may contain cracks that first appeared when the original mud was drying out.