The first step involves determining the texture of your unknown rock sample. There are five basic textural types, phaneritic, aphanitic, glassy, vesicular and fragmental. Examples of each are shown below. Remember, many rocks have a porphyritic texture (two different grain sizes). But in reality, we treat porphyritic textured rocks as either phaneritic or aphanitic depending on size of the smallest of the two different grain sizes. Most porphyritic textures rocks end up in the aphanitic group, but rarely we do see a porphyritic phaneritic rock. Let's examine your rock. CLICK on the appropriate texture to move to the next identification step.

Phaneritic (coarse-grained) texture. All of the mineral grains should be visible with the unaided eye.
Aphanitic (fine-grained) texture. Most or all of the mineral grains cannot be seen with the unaided eye.
Glassy texture. No mineral grains are present, the rock is comprised entirely of glass.
Vesicular texture. No mineral grains are present, the rock is light-weight and contains numerous holes or cavities.
Fragmental texture. Rock fragments and glass shards embedded in a fine-grained (ash) matrix.