Types of structures Found in Igneous Rocks
- Structures due to Mobility of Magma or Lava Flow structure Pillow Structure Ropy and Blocky Lava Spherulitic structure Orbicular structure
- Structures due to cooling of Magma The jointing structure Rift and Grain Vesicular Structure Miarolitic structure
- Miscellaneous structures Reaction Structure Xenolithic structure
What are the structure and texture of igneous rock?
An igneous rock is any crystalline or glassy rock that forms from cooling of a magma. 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.
What are the structures of igneous rocks differentiate each?
The two main categories of igneous rocks are extrusive and intrusive. Extrusive rocks are formed on the surface of the Earth from lava, which is magma that has emerged from underground. Intrusive rocks are formed from magma that cools and solidifies within the crust of the planet.
What are the 5 intrusive igneous rock structures?
Intrusive StructuresDikes. A dike is an intrusive rock that generally occupies a discordant, or cross‐cutting, crack or fracture that crosses the trend of layering in the country rock. ... Sills. ... Laccoliths. ... Volcanic necks. ... Plutons.
What are the two different types of igneous rock structures?
Igneous rocks are divided into two groups, intrusive or extrusive, depending upon where the molten rock solidifies.
What are the main characteristics of igneous rocks?
Characteristics of Igneous RocksThe igneous form of rocks does not include any fossil deposits. ... Most igneous forms include more than one mineral deposit.They can be either glassy or coarse.These usually do not react with acids.The mineral deposits are available in the form of patches with different sizes.
What are the 4 classifications of igneous rocks?
Igneous rocks can be divided into four categories based on their chemical composition: felsic, intermediate, mafic, and ultramafic.
What are the 3 types of intrusive rock?
Three common types of intrusion are sills, dykes, and batholiths (see image below).
What are the example of igneous rock?
There are two basic types: 1) intrusive igneous rocks such as diorite, gabbro, granite and pegmatite that solidify below the Earth's surface; and 2) extrusive igneous rocks such as andesite, basalt, obsidian, pumice, rhyolite and scoria that solidify on or above the Earth's surface.
What type of rock is an igneous rock?
Igneous rock (derived from the Latin word ignis meaning fire), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or lava.
What is structure in rocks?
The design and structure of the rocks is defined as the nature and properties of the rocks from the respective minerals and rock formations. The texture is characterized by its shape and minerality; The structure, characterized by its alignment, consists of rock elements.
What is the structure of sedimentary rocks?
Sedimentary structures include features like bedding, ripple marks, fossil tracks and trails, and mud cracks. They conventionally are subdivided into categories based on mode of genesis. Structures that are produced at the same time as the sedimentary rock in which they occur are called primary sedimentary structures.
What is the structure of metamorphic rocks?
Metamorphic rocks are often intimately related to large-scale (kilometres of tens of kilometres) structural features of Earth. Such features include folds, nappes, and faults with a wide variety of geometries.
What are the 4 types of sedimentary structures?
Sedimentary structures include features like bedding, ripple marks, fossil tracks and trails, and mud cracks.
What is structure in rocks?
The design and structure of the rocks is defined as the nature and properties of the rocks from the respective minerals and rock formations. The texture is characterized by its shape and minerality; The structure, characterized by its alignment, consists of rock elements.
What is the structure of metamorphic rocks?
Metamorphic rocks are often intimately related to large-scale (kilometres of tens of kilometres) structural features of Earth. Such features include folds, nappes, and faults with a wide variety of geometries.
What are the differences between volcanic and plutonic rocks?
The two main types of igneous rocks are plutonic rocks and volcanic rocks. Plutonic rocks are formed when magma cools and solidifies underground. Volcanic rocks are formed from lava that flows on the surface of the Earth and other planets and then cools and solidifies.
What is the structure of an igneous rock?
The structure of an igneous rock is normally taken to comprise the mutual relationships of mineral or mineral-glass aggregates that have contrasting textures, along with layering, fractures, and other larger-scale features that transect or bound such aggregates. Structure often can be described only in relation to masses ...
What percentage of crustal rocks are igneous?
Clarke estimated that 95 percent of crustal rocks are of igneous origin (formed from molten silicate masses, or magmas).
What are lithophysae made of?
Lithophysae, also known as stone bubbles, consist of concentric shells of finely crystalline alkali feldspar separated by empty spaces; thus, they resemble an onion or a newly blooming rose. Commonly associated with spherulites in glassy and partly crystalline volcanic rocks of salic composition, many lithophysae are about the size of walnuts. They have been ascribed to short episodes of rapid crystallization, alternating with periods of gas escape when the open spaces were developed by thrusting the feldspathic shells apart or by contraction associated with cooling. The curving cavities commonly are lined with tiny crystals of quartz, tridymite, feldspar, topaz, or other minerals deposited from the gases.
What is orbicular rock?
The term orbicular is applied to rounded, onionlike masses with distinct concentric layering that are distributed in various ways through otherwise normal-appearing phaneritic rocks of silicic to mafic composition. The layers within individual masses are typically thin, irregular, and sharply defined, and each differs from its immediate neighbours in composition or texture. Some layers contain tabular or prismatic mineral grains that are oriented radially with respect to the containing orbicule and, hence, are analogous to spherulitic layers in volcanic rocks. The minerals of most orbicules are the same as those of the enclosing rock, but they are not necessarily present in the same proportions. The concentric structure appears to reflect rhythmic crystallization about specific centres, commonly at early stages in consolidation of the general rock mass.
What are the crystals in a glassy rock?
The curving cavities commonly are lined with tiny crystals of quartz, tridymite, feldspar, topaz, or other minerals deposited from the gases. Some glassy rocks of silicic composition are marked by domains of strongly curved, concentrically disposed fractures that promote breakage into rounded masses of pinhead to walnut size.
What is the concentric structure of plutonic rock?
The concentric structure appears to reflect rhythmic crystallization about specific centres, commonly at early stages in consolidation of the general rock mass. The normal fabric of some relatively coarse-grained plutonic rocks is interrupted by clusters of crystals with radial grouping but without concentric layering.
What is the origin of crustal rocks?
Clarke estimated that 95 percent of crustal rocks are of igneous origin (formed from molten silicate masses, or magmas). Sedimentary rocks... Many vesicles have been partly or completely filled with quartz, chalcedony, opal, calcite, epidote, zeolites, or other minerals. These fillings are known as amygdules, and the rock in which they are present ...
How do igneous rocks form?
Igneous rocks (from the Greek word for "fire") form when hot, molten rock (magma) crystallizes and solidifies. Magma originates deep within the Earth, near active plate boundaries or hot spots. Magma that rises to the surface is called lava. Igneous rocks are classified into two groups depending upon where the molten rock solidifies: Extrusive ...
What is the name of the rock that has abundant light colored minerals?
Felsic: Derived from the words feldspar and silica to describe an igneous rock having abundant light-colored minerals such as quartz, feldspars, or muscovite.
What is diorite rock?
Diorite is a classic "salt and pepper" rock with a phaneritic texture.
What are phenocrysts of obsidian surrounded by?
In this specimen of rhyolite porphyry, phenocrysts of obsidian are surrounded by a fine matrix.
How long does it take for magma to cool?
The magma cools very slowly over many thousands or millions of years until is solidifies. Slow cooling means the individual mineral grains have a very long time to grow, forming a rock with large, visible crystals. National parks with excellent examples of intrusive igneous rocks include:
What is the texture of igneous rocks?
Microcrystalline: The texture of igneous rocks is said to be microcrystalline if the crystals are clearly distinguishable only under microscope.
How are igneous rocks formed?
Igneous rocks are one of the three main rock types, others being sedimentary and metamorphic. They are formed through the cooling and solidification of magma or lave. They may form with or without crystallization, either below the surface of earth as intrusive (plutonic) rocks or on the surface of earth as extrusive (volcanic) rocks.
Why are igneous rocks aphanitic?
Igneous rocks are said to be aphanitic if the crystals cannot be seen with unaided eye. This type of texture is formed as a result of rapid rate of cooling. The crystals are microscopic and may contain vesicles (holes from gas bubbles). They are of following types:
What is the vesicular structure?
Vesicular and amygdaloidal structures: Near the top of the flows, empty cavities of variable dimensions are formed due to lavas with gases and other volatiles. The individual cavity is called the vesicles and as a whole resulted structure is called the vesicular structure. The empty cavities filled by secondary minerals are called the amygdales. The lavas with amygdales are said to have an amygdaloidal structure.
What is the horizontal slice of igneous rock?
Sheet Structure: The horizontal slices developed on the massive igneous rock due to one set of well-defined jointing is called the sheet structure of igneous rocks.
What is a ropy lava?
Ropy Lava: A very smooth surface developed during basic lava flows due to their low viscosity. They are also known as the ‘Pahoehoe’ structures.
What is a hollow structure developed due to the brain out of interior fluid lava?
Lava Drain Tunnels: It is a hollow structure developed due to the brain out of interior fluid lava.
What are the structures found in igneous rocks?
Types of structures Found in Igneous Rocks. Structure refers to the large scale features which develop in the body of extrusion or intrusion. They may so well develop that they can recognize with visual inspection or they may become apparent only. When thin sections of such rocks examine under a microscope.
What are Igneous Rocks?
All rocks which have been formed from an originally hot molten material by the process of cooling and crystallization are defined as Igneous Rocks.
What are undersaturated rocks?
Undersaturated Rocks. These are silica deficient rocks containing the percentage of silica less than 44%. Due to insufficient silica, they contain undersaturated minerals like leucite, nepheline, sodalite olivine, etc.
What is the chemical composition of igneous rocks?
For example, rocks like granite may contain about 70-80% of silica and very little quantity of iron, magnesia, and lime, while on the other hand rocks like peridotite contain only 35-40% of silica and larger quantities of iron, magnesia, and lime.
What is the hot molten material from which igneous rocks are believed to form?
The hot molten material from which igneous rocks are believed to form is called magma. When occurring below the surface of the Earth, and it is called lava when erupted through volcanoes. Magma or lava from which igneous rocks form may not be entirely a pure melt, it may have a crystalline or solid fraction and also a gaseous fraction thoroughly ...
What percentage of rocks contain silica?
Saturated rocks. These rocks contain a percentage of silica between 44-66%. They contain just sufficient silica to form stable silicate minerals but no free quartz. Rocks containing silica percentage between 52-66% categorize as intermediate rocks.
Which method is the most accurate for determining the relative proportions of igneous rocks?
The mineralogical classification rocks are the most convenient and more accurate method of classification of igneous rocks. When the mineralogical composition of a parent magma and cooling history of the rock. Further, minerals in rocks can easily identify and their relative proportions can be ascertained with reasonable accuracy.
What are the characteristics of igneous rocks?
Characteristics of Igneous Rocks 1 The igneous form of rocks does not include any fossil deposits. If there are any chances of fossil deep inside the crust, it erupts out of the Earth’s surface and gets destroyed due to the sheer heat these rocks produce. 2 Most igneous forms include more than one mineral deposit. 3 They can be either glassy or coarse. 4 These usually do not react with acids. 5 The mineral deposits are available in the form of patches with different sizes.
What are Igneous Rocks?
Igneous rocks are defined as types of rocks that are formed when molten rock (rock liquefied by intense heat and pressure) cools to a solid state.
What are intrusive igneous rocks?
Intrusive igneous rocks are rocks that crystallize below the earth’s surface resulting in large crystals as the cooling takes place slowly. Diorite, granite, pegmatite are examples of intrusive igneous rocks.
What does it mean when a rock has a large crystal?
Larger crystals generally indicate intrusive igneous rocks. Smaller crystals generally indicate faster cooling associated with extrusive igneous rocks. Types of Igneous Rock Texture.
How to identify igneous rocks?
Igneous rocks can be easily identified with their texture, density, colour, and mineral composition. Its texture depends on the shape, size, time period to cool down and solidify, and the arrangement of crystals in the rock.
How are sedimentary rocks formed?
Sedimentary rocks are formed by the accumulation or deposition of mineral or organic particles at the Earth’s surface while metamorphic rocks are formed when watery hot fluids are subjected to high heat and pressure, lastly, igneous rocks are formed when lava cools and solidifies.
What is a pyroclastic deposit?
Pyroclastic deposits are accumulations of fragmented material (e.g. ash, bombs, tuffs, and volcanic breccias) ejected during volcanic eruptions. As igneous rocks are formed from magma and begin the rock cycle, they are called primary rocks. Igneous rocks can be easily identified with their texture, density, colour, and mineral composition.
How are igneous rocks classified?
Igneous rocks are classified on the basis of mineralogy, chemistry, and texture. As discussed earlier, texture is used to subdivide igneous rocks into two major groups: (1) the plutonic rocks, with mineral grain sizes that are visible to the naked eye, and (2) the volcanic and hypabyssal types, which are usually too fine-grained or glassy for their mineral composition to be observed without the use of a petrographic microscope. Being rather coarsely grained, phaneritic rocks readily lend themselves to a classification based on mineralogy since their individual mineral components can be discerned, but the volcanic rocks are more difficult to classify because either their mineral composition is not visible or the rock has not fully crystallized owing to fast cooling. As a consequence, various methods employ chemical composition as the criterion for volcanic igneous rock classification. A commonly used technique was introduced at the beginning of the 20th century by the American geologists C. Whitman Cross, Joseph P. Iddings, Louis V. Pirsson, and Henry S. Washington. In this method, the mineral composition of the rock is recalculated into a standard set of typically occurring minerals that theoretically could have developed from the complete equilibrium crystallization at low temperatures of a magma of the indicated bulk composition. The calculated hypothetical mineral composition is called the norm, and the minerals constituting the standard set are termed normative minerals, since they are ordinarily found in igneous rocks. The rock under analysis may then be classified according to the calculated proportions of the normative minerals.
What are the edges of igneous rock?
These are arrangements of rock units with contrasting composition, or texture, in an igneous body, commonly in a broadly concentric pattern. Chilled margins, the fine-grained or glassy edges along the borders of many extrusive and shallow-seated intrusive bodies, represent quenching of magma along contacts with cooler country rock. Other kinds of zones generally reflect fractional crystallization of magma and are useful in tracing courses of magmatic differentiation, as will be noted later.
What are the zones of plutonic rocks?
Among the plutonic rocks, they appear chiefly as local to very extensive zones of pervasive shearing, dislocation, and granulation, commonly best recognized under the microscope. Those developed prior to final consolidation of the rock are termed protoclastic; those developed after final consolidation, cataclastic.
What are flow structures?
Flow structures. These are planar or linear features that result from flowage of magma with or without contained crystals. Various forms of faintly to sharply defined layering and lining typically reflect compositional or textural inhomogeneities, and they often are accentuated by concentrations or preferred orientation of crystals, inclusions, ...
What are inclusions in magma?
These are special types of inclusions that are intimately related to their host rocks and in general are relatively rich in one or more of the host-rock minerals. They range from small pods to extensive layers and from early-stage crystal accumulations formed by gravitational settling in magma to very late-stage concentrations of coarse-grained material developed in place.
What is a rounded mass of solid material enclosed within a rock of recognizably different composition or texture?
These are rounded to angular masses of solid material enclosed within a rock of recognizably different composition or texture. Those consisting of older material not directly related to that of their host are known as xenoliths, and those representing broken-up and detached older parts of the same igneous body that encloses them are termed cognate ...
What type of structure has alternating light and dark bands?
An interesting type of zonal structure is an orbicular configuration that has alternating light and dark repeating bands in an oval arrangement found in some diorites and granodiorites. Pegmatites also often have zonal structures due to fluctuations in fluid composition. This results in “pockets” that may contain gems or other unusual minerals.
