L> Igneous absent composition and texture ask GeoMan... exactly how do composition and texture relate to igneous rocks? Igneous rocks space crystalline solids i m sorry cool native magma: the fluid phase of heavy rock. Magmas happen at depth in the crust, and are stated to exist in "magma chambers," a rather loosened term describe an area whereby the temperature is great enough to melt the rock, and the pressure is low enough to enable the product to expand and also exist in the fluid state. Numerous different types of igneous rocks have the right to be produced. The key factors to usage in determining which absent you have actually are the rock"s texture and composition. Texture texture relates to how huge the separation, personal, instance mineral grains room in the final, hard rock. In many cases, the resulting grain size depends on how easily the magma cooled. In general, the slow the cooling, the bigger the crystals in the final rock. Due to the fact that of this, we assume that coarse grained igneous rocks room "intrusive," in the they cooled at depth in the crust where they were insulated by layers of rock and also sediment. Fine grained rocks are dubbed "extrusive" and are generally created through volcanic eruptions. Grain size can vary greatly, from exceptionally coarse grained rocks with crystals the dimension of your fist, under to glassy material which cooled so easily that there are no mineral grains at all. Rough circuit grain ranges (with mineral grains large enough to view without a magnifying glass) are called phaneritic. Granite and also gabbro are examples of phaneritic igneous rocks. Well grained rocks, where the separation, personal, instance grains are too little to see, are called aphanitic. Basalt is an example. The most usual glassy rock is obsidian. Obviously, there room innumerable intermediate stages to confuse the issue. ingredient The other element is composition: the aspects in the magma directly influence which mineral are developed when the magma cools. Again, us will describe the extremes, but there are numerous intermediate compositions. (Composition relates to the mafic and also felsic terms disputed in one more question. If this terms are confusing, please describe that discussion before continuing.) The composition of igneous magmas is straight related to whereby the magma is formed. Magmas associated with crustal spreading are generally mafic, and also produce basalt if the magma erupts in ~ the surface, or gabbro if the magma never ever makes it out of the magma chamber. That is important to remember the basalt and gabbro room two different rocks based completely on textural distinctions - they are compositionally the same. Intermediate and felsic magmas are associated with crustal compression and also subduction. In this areas, mafic seafloor basalt and also continental sediments room subducted back into the crust, where they re-melt. This allows the differentiation process to continue, and also the result magma is enriched in the lighter elements. Intermediary magmas create diorite (intrusive) and andesite (extrusive). Felsic magmas, the final purified result of the differentiation process, result in the formation of granite (intrusive) or rhyolite (extrusive).


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Click below for a chart summarizing the category of igneous rocks.