How to Identify Rock Textures

You will not use your hands to identify rock textures, but rather your eyes. While you can certainly learn to identify rock textures in the wild, you may find it helpful to sit down with some samples. First, it is important to realize that rock textures do not refer to the smoothness or roughness of the rock's surface. Rock texture is a specific reference to the size of the crystals that formed the sample of rock. Take a careful look at your igneous rock samples. There are several different rock texture types, with distinct traits of their own. Rock texture may also be called rock microstructure, and, along with color and hardness, can help you determine the type of rock and its properties.

Make sure that all of your rock samples are clean. Soap, water and an old cloth will work fine for removing dirt and debris. These can be purchased at a dealer, rock or bead shop or simply collected when hiking or climbing. Be sure to follow all local laws if collecting rock samples. Igneous rocks you might purchase or collect in order to learn how to identify rock textures include basalt, granite, diorite and others.

Examine your rock samples with the naked eye. You may first notice that some of your rocks, especially if you bought them rather than found them, have a noticeable sparkle. This is the first clue that you are looking at pegmatite rock textures. Granite and diorite pegmatites are examples of a pegmatitic texture. You will see very large crystals in these rocks. These crystals are larger than 20 mm across and are clearly visible to the naked eye without magnification. Crystals over 10 meters across have been found in igneous rock with a pegmatitic texture. Rock textures in this case are typically composed of feldspar, mica and quartz, all identifiable by color.

Take a closer look at your samples now, once you have identified the pegmatite textures. If you do not see very large crystals in your rock samples, you are likely looking at a stone with a Phaneritic texture. This is present when crystals are visible to the naked eye, but smaller than 20 mm across. The mineral grains in the rock will be visible, either quite clearly or as a speckled pattern without using a magnifying glass. The surface of the rock will be quite coarse to the touch. Most granites and diorites show a phaneritic rock texture upon examination, as well as gabbro and dunite. This is one of the most common surfaces climbers encounter, and while climbing Phaneritic rocks can be a challenge, they are a popular choice. Identifying the texture of your climbing surface can help you make smart decisions on your trek.

Take out your magnifying glass to learn more about identifying rock textures. If your igneous rock samples do not have clearly visible crystals when you examine then without a magnifying glass, you should take a look at them with some level of magnification. You are likely looking at an aphanitic rock texture with a fine grained appearance. The crystalline structures are fine enough to not be seen by the naked eye, but should be visible with some magnification. Basalt is the best known common rock with this sort of rock texture.

Handle your rock samples to explore the variety of types of igneous rock you could encounter when climbing and better understand their properties. Upon examination of your rock samples, you may see other rock textures, either with or without magnification. A porphyritic rock texture shows a combination of visible crystals in the rock and an overall fine grained rock texture. Basalt, andesite and rhyolite are all found with this unusual combination of rock textures. Keep in mind that this rock texture may pose additional challenges for climbers.

Look through your rock samples to see if you can find some of the less common rock textures. Glassy texture is an apt description for the next rock texture used in classifying igneous rocks. A glassy textured rock is composed entirely of glass. Very few crystals will be visible in the rock. Obsidian and basaltic glass are examples of this type of rock texture. Vesicular rock textures are produced when lava solidifies with bubbles of gas still present inside. The rock will have an unusual bubbly rock texture, as seen in pumice. Finally, pyroclastic rock texture is used to refer to rock composed entirely of volcanic fragments, as is seen in volcanic tuff. These rock textures are less common, and climbers will likely never need to identify these types of igneous rocks.