Sandstone

Sandstones are made of sand grains that have been cemented together. Like sandpaper, sandstones usually have a rough, granular texture, but to really identify a sandstone you have to peer closely at its surface and look for individual sand grains. Since the grain diameters range from 2 mm all the way down to only 0.06 mm, you may need a good magnifying lense to see the sand grains in a fine-grained sandstone.

The sandy texture of sandstone is easiest to see when the sand grains are highlighted by different colors. The grains are harder to see in the lower, rust-stained part of this rock.
This view is as close as most beginners seem to want to get to a rock. You can just make out the grainy texture of the sandstone. Click to enlarge. The upper part of the rock shows faint horizontal layering, whereas the bottom shows faint crossbeds.
This is the same rock as above, but with the close-up look that geologists use. Now you can see the tiny sand grains that make up the rock. Geologists take a very close look because they learn young that it is easy to be fooled by the superficial appearance of a rock. Sandstones exposed near Etna, PA
This close-up of the Loyalhanna Sandstone of southwestern PA shows gray quartz grains surrounded by white calcite cement. It's easy to see the sand grains in this rock. Click to enlarge, and visit the Sedimentary Minerals page to see the super close-up.
Most samples that you see in geology labs do not show obvious layering. This is an example in which the layering is highlighted by concentrations of carbonized plant debris (black). Photo taken west of Pittsburgh (US 60).

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