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. There are six main types of textures; phaneritic, aphanitic, porphyritic, glassy, pyroclastic and pegmatitic.
Herein, what are the three types of igneous bodies?
The most common types of igneous rocks are:
dolerite (also called diabase)
What are the features of igneous rocks?
Igneous rocks form from the solidification of magma (molten rock). A reminder: magma is molten rock beneath the Earth’s surface and lava is magma that is on the Earth’s surface. The main characteristics of an Igneous rock are crystal size (grain size) and texture.
What are the four textures of igneous rocks?
Igneous Rock Textures
COARSE GRAINED TEXTURE (PHANERITIC), mineral grains easily visible (grains several mm in size or larger)
B) FINE GRAINED TEXTURE (APHANITIC), mineral grains smaller than 1mm (need hand lens or microscope to see minerals)
C) PORPHYRITIC TEXTURE (MIXED FINE AND COARSE)
D) GLASSY TEXTURE (NO CRYSTALS VISIBLE)
How are igneous rocks classified according to composition and texture?
Igneous rocks may be simply classified according to their chemical/mineral composition as felsic, intermediate, mafic, and ultramafic, and by texture or grain size: intrusive rocks are course grained (all crystals are visible to the naked eye) while extrusive rocks may be fine-grained (microscopic crystals) or glass (
How do igneous rocks with porphyritic textures form?
Porphyritic rocks are formed when a column of rising magma is cooled in two stages. In the first stage, the magma is cooled slowly deep in the crust, creating the large crystal grains, with a diameter of 2 mm or more.
What is the texture of an intrusive igneous rock?
Igneous rocks which form by the crystallization of magma at the surface of the Earth are called extrusive rocks. They are characterized by fine-grained textures because their rapid cooling at or near the surface did not provide enough time for large crystals to grow.
How does the cooling rate affect the grain size of igneous rocks?
Topic. The activity relates to the process of igneous rock formation by the cooling of magma. It can be used to illustrate how the rate at which molten rock cools affects the size of the crystals that form within the solid rock – rapid cooling producing small crystals, slower cooling producing larger ones.
What is a vesicular texture?
Vesicular texture is a volcanic rock texture characterized by a rock being pitted with many cavities (known as vesicles) at its surface and inside. This texture is common in aphanitic, or glassy, igneous rocks that have come to the surface of the earth, a process known as extrusion.
What is sediment texture?
Sediment texture refers to the shape, size and three-dimensional arrangement of the particles that make up sediment or a sedimentary rock.
Why are some igneous rocks darker than others?
Slow cooling magma forms coarse-grained rock with large crystals. Why are some igneous rocks dark and others light? Because it depends on the silica content in the lava or magma. Magma that is high in silica usually forms light-colored rocks, such as granite.
What is the texture of a metamorphic rock?
TEXTURES Textures of metamorphic rocks fall into two broad groups, FOLIATED and NON-FOLIATED. Foliation is produced in a rock by the parallel alignment of platy minerals (e.g., muscovite, biotite, chlorite), needle-like minerals (e.g., hornblende), or tabular minerals (e.g., feldspars).
Which igneous rock has a vesicular texture and a felsic composition?
Classification of Igneous RocksTEXTUREFelsicMaficPhaneriticGraniteGabbroAphaniticRhyoliteBasaltVesicularPumiceScoriaGlassyObsidian
What is a Aphanitic texture?
Fine-Grained (Aphanitic) Textures. Fine-grained textures generally indicate magmas that rapidly cooled at or near the Earth’s surface. Fast cooling prevents crystals from growing very large. The cutoff between fine- and coarse-grained textures is about 1 mm.
What controls the size of the crystals in an igneous rock?
If the magma cools slowly, then the crystals have enough time to grow and become large. Some granites contain minerals which are up to one meter (3 ft) across! The size of crystals in an igneous rock is an important indicator of the conditions where the rock formed.
What is the grain size of granite?
Granite: The specimen above is a typical granite. It is about two inches across. The grain size is coarse enough to allow recognition of the major minerals. The pink grains are orthoclase feldspar, and the clear to smoky grains are quartz or muscovite.
Are Phaneritic rocks intrusive or extrusive?
Extrusive igneous rocks form after lava cools above the surface. Extrusive igneous rocks cool much more rapidly than intrusive rocks. There is little time for crystals to form, so extrusive igneous rocks have tiny crystals (Figure below). Cooled lava forms basalt with no visible crystals.
What are the criteria you use to classify igneous rocks?
From this often confusing situation, a commonly used classification for igneous rocks has emerged based on two criteria–texture and chemical composition. Texture refers to the size of crystals, presence of glass, and porosity of the rock. Texture is determined primarily by how the magma or lava cooled.
How do you identify an igneous rock?
Igneous rocks are rocks which solidify from molten material (magma). Cooling of the magma can occur beneath the surface (plutonic) or on the surface (volcanic). Igneous rocks can be identified by the determination of the composition and texture of the rock.
What does the color of an igneous rock tell us?
The color index of an igneous rock is a measure of the ratio of dark colored, or mafic, minerals to light colored, or felsic, minerals. According to Bowen’s Reaction series, minerals crystallize at different temperatures depending on their chemical composition.
How are obsidian rocks formed?
Obsidian is a naturally occurring volcanic glass formed as an extrusive igneous rock. Obsidian is produced when felsic lava extruded from a volcano cools rapidly with minimal crystal growth.
How do you classify a sedimentary rock?
Sedimentary rocks form at the Earth’s surface. Geologists divide sedimentary rocks into two major types, based on what they are made of and how they form. Clastic sedimentary rocks are composed of pieces of rock, minerals, or fossils that have been cemented together. Sandstone is an example.
Why are lava flows typically finer grained than intrusive igneous rocks?
Lava flows are typically finer grained than intrusive igneous rocks. Why? Intrusive magma is cooler because it is well insulated by the surrounding rock. The extrusive magma, because it is deep below the surface, cools very slowly producing very small mineral grains.