Glassy Texture Igneous Rocks

In our simplified classification of the common igneous rocks we will recognize obsidian as the only rock of glassy texture. Superficially a glassy texture suggests cooling that was so extremely fast that no crystals could form. Igneous textures include the rock textures occurring in igneous rocks igneous textures are used by geologists in determining the mode of origin igneous rocks and are used in rock classification.

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However composition is also vitally important.

Glassy texture igneous rocks. Slower cooling either beneath earth s surface or within very thick masses of lava promotes the formation of crystals and under favourable circumstances of magma composition and other factors. But dark rocks like gabrro are more problematic. A pattern of breakage of glass differs from patterns of breakage of other igneous rock. Phaneritic fan a rit ic rocks have mineral grains that are large enough to be seen with the naked eye or a hand lens like this granite.

There are six main types of textures. The high silica sio 2 concentrations found in felsic rocks rhyolite composition causes a rock to form a glass much more readily than it would in low silica rocks such as basalt. Aphanitic a not phaner visible rocks in contrast to phaneritic rocks typically form. A particularly distinctive breakage pattern of obsidian is conchoidal fracture.

A crystal or crystalline solid is a solid material whose constituents such as atoms molecules or ions are arranged in a highly ordered microscopic structure. Magma can cool to form an igneous rock either on the surface of the earth. Let s start with some definitions. For the more felsic rocks like granite phaneritic texture is rarely misidentified.

Introduction to igneous rocks. A magma consists mostly of liquid rock matter but may contain crystals of various minerals and may contain a gas phase that may be dissolved in the liquid or may be present as a separate gas phase. An igneous rock is any crystalline or glassy rock that forms from cooling of a magma. Phaneritic texture james st.

Igneous textures include the rock textures occurring in igneous rocks igneous textures are used by geologists in determining the mode of origin igneous rocks and are used in rock classification. A good rule of thumb is that fine grained or aphanitic rocks are dull appearing while phaneritic rocks are brighter or shinier of course be careful of a glassy rock like obsidian. There are six main types of textures. Pumice is another type of igneous rock with a glassy texture.

Phaneritic aphanitic porphyritic glassy pyroclastic and pegmatitic. Some igneous rocks are very smooth and glassy obsidian while others have a very rough texture such as the rocks used on the bottom of a propane gas grill. Microscopic structure of halite see crystal wik. Phaneritic aphanitic porphyritic glassy pyroclastic and pegmatitic.

Aphanitic and glassy textures represent relatively rapid cooling of magma and hence are found mainly among the volcanic rocks.