What is the difference between andesite and diorite

Pavlof Volcano - plate tectonics: Simplified plate tectonics cross-section showing how Pavlof Volcano is located in the Aleutian Island chain, above a subduction zone, where basaltic crust of the Pacific Plate is being partially melted at depth. The ascending magma then passes through continental crust of the North America Plate, where it might mix with other magmas or be altered by melting rocks of different composition.

Andesite derives its name from the Andes Mountains of South America. In the Andes it occurs as lava flows interbedded with ash and tuff deposits on the steep flanks of stratovolcanoes. Andesite can also form away from the subduction zone environment. For example, it can form at ocean ridges and oceanic hot spots from partial melting of basaltic rocks. It can also form during eruptions at continental plate interiors where deep-source magma melts continental crust or mixes with continental magmas.

There are many other environments where andesite might form. Hornblende Andesite Porphyry: A specimen of andesite with large visible hornblende phenocrysts. This type of rock could be called an "andesite porphyry" because of its texture. It could also be called a "hornblende andesite" because of its composition.

Photo by NASA. Occasionally, andesites contain large, visible grains of plagioclase, amphibole, or pyroxene. These large crystals are known as "phenocrysts. These high-crystallization-temperature minerals begin forming below the surface and grow to visible sizes before the magma erupts. When the magma erupts onto the Earth's surface, the rest of the melt crystallizes quickly.

This produces a rock with two different crystal sizes: large crystals that formed slowly at depth the "phenocrysts" , and small crystals that formed quickly at the surface known as "groundmass". The name of an abundant phenocryst mineral may be used as an adjective to the rock name. An example is the hornblende andesite porphyry shown in the accompanying photo. Andesite outcrop: Close view of an andesite lava flow at Brokeoff Volcano in California.

Photo by the United States Geological Survey. The best way to learn about rocks is to have specimens available for testing and examination. Some magmas that produce explosive eruptions above subduction zones contain enormous amounts of dissolved gas.

These magmas can contain several percent dissolved gas by weight! This gas can have several origins, examples of which include the following:. At depth, these gases can be dissolved in the magma like carbon dioxide dissolved in a can of cold beer. If that can of beer is shaken and suddenly depressurized by opening the can, the gas and the beer will erupt from the opening. A volcano behaves in a similar manner. A rising magma chamber can instantly be depressurized by a landslide, faulting, or other event and an enormous volume of rapidly expanding gas will explode through the overlying rock.

Many volcanic plumes and ash eruptions occur when gas-charged andesitic magmas erupt. The gas pressure that causes the eruption blows large amounts of tiny rock and magma particles into the atmosphere. Streak of rock is the color of powder produced when it is dragged across an unweathered surface. The streak of Andesite is white while that of Diorite is bluish black.

The specific heat capacity of Andesite is 2. Depending on the properties like hardness, toughness, specific heat capacity, porosity etc. Andesite is heat resistant, pressure resistant, wear resistant whereas Diorite is heat resistant, pressure resistant, wear resistant.

A softUsvista venture! Igneous Rocks -. Basaltic Trachyandesite. Compare Rocks. Andesite vs Diorite. From early 19th century coined in French, formed irregularly from Greek diorizein distinguish. Andesite is a fine-grained igneous rock that forms when the magma is erupted onto the surface and is crystallized quickly.

Banded iron for.. Compare Igneous Rocks » More. Andesite vs Granodiorite. Andesite vs Amphibolite. Andesite vs Pegmatite. By quantity, these are the by far most common rock types. Most magmas actually never reach the surface of the earth. The basic classification is the same as for plutonic rocks: with increasing silica content, they include: basalt, andesites, dacites, rhyolite, pumice and obsidian.

Main types of igneous rocks The most widely used and simplest classification of igneous rocks is according to the silica SiO 2 content in the bulk rock composition.

Wikimedia Commons. Diorite sample image: Michael C. Rygel via Wikimedia Commons.