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Aphaniteis the name of some igneous rocks with fine-grained component mineral crystals which are invisible to the normal eye. This type of texture is as a result of rapid cooling in volcanic or in hypabyssal environments. However, the texture of aphanitic textures are not the same as that of the volcanic glass which has a much finer grained surface than aphanitic rocks. It is considered to have an appearance like glass or glass-like.

Basalt formed from surface lava usually exhibits an aphanitic texture. It is also regarded as an "extrusive" rock since while being formed there is not enough time for large crystals to grow. Aphanitic rocks are divided into general terms such as light, dark or intermediate in colour since the crystals of the individual minerals cannot easily be resolved.

As a result of the rapid cooling condition voids are often present in aphanitic rock, this caused by escaping gases from the lava flow and would be most seen in the upper portions of the lava flow. They are made up of plagioclase feldspar, with augite or hornblende and may also contain quartz, biotite and a small amount of orthoclase.

Aphanites represent a texture of igneous rock. There are three main classifications of rocks, igneous rocks, sedimentary rocks and metamorphic rocks. The rock that is considered to have morphed out either igneous or sedimentary rock is known as metamorphic rock, while sedimentary rock as the name implies evolved from the sedimentation of materials on the surface of the earth in different water bodies.

Igneous rocks are formed mainly in three places; where plates come together at the subduction zones, where lithospheric plates are pulled apart at the mid-ocean ridges and where the continental crust is pushed together. This makes it thicker whilst also allowing it to heat up into melting.

Additional Resources

Apatite   Aplite   Basalt

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