How Do Igneous Rocks Form?
ES0603  Describing Rock Textures

Your description of the rocks probably included their color and surface shape, plus characteristics such as size, shape, and arrangement of the grains or crystals in each rock. The characteristics related to grain size are known as a rock's texture—coarse-grained, fine-grained, and glassy are all descriptions of a rock's texture. The texture of igneous rocks can be analyzed to understand how the rock became solid or crystallized from liquid, melted rock.

  !   Click each image to see a larger version plus information about the rock's texture. Add details to your answers for question 1.

Coarse-grained texture
Glassy texture
Porphyritic texture
Fine-grained texture
Matthew Nyman, TERC

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