What is the characteristics of plutonic rocks?
The main way to tell a plutonic rock is that it’s made of tightly packed mineral grains of medium size (1 to 5 mm) or larger, which means that it has phaneritic texture. In addition, the grains are of roughly equal size, meaning that it has an equigranular or granular texture.
Why do plutonic and volcanic rocks have different textures?
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. The texture of an igneous rock depends on the size of the crystals in the rock.
Which are minerals considered for Iugs classification of plutonic igneous rocks?
The QAPF diagram utilizes four minerals, or mineral groups, to classify igneous rocks. These minerals are quartz (Q), Alkali feldspars (A), plagioclase feldspars (P), and feldspathoids (F). F and Q cannot form in plutonic rocks simultaneously due to the difference in their respective silica contents.
What is Iugs classification of igneous rock?
The classification separates and individually classifies the pyroclastic, carbonatitic, melititic, lamprophyric and charnockitic rocks before entering the main QAPF classification for plutonic and volcanic rocks which is based on the modal mineral proportions of quartz (Q), alkali feldspar (A) and plagioclase (P) or of …
What is the texture of a plutonic rock?
Plutonic rocks form when magma cools within the Earth’s crust. The rate of cooling of the magma is slow, allowing large crystals to grow. Plutonic rocks are characteristically coarse-grained.
How are plutonic rocks classified?
Igneous rocks may be divided into two categories. Intrusive or plutonic rocks crystallize from magma beneath the earth’s surface. Extrusive or volcanic rocks crystallize from lava at the earth’s surface. In addition to texture, igneous rocks may are classified according to their chemical composition.
What is the difference in texture between plutonic and volcanic igneous rocks?
Plutonic rocks are coarse-grained as they are formed slowly that allows the formation of large crystals before the magma solidifies into a rock. Volcanic rocks are igneous rocks that are formed above the ground from the lava.
What are the textures of igneous rocks?
Igneous textures are used by geologists in determining the mode of origin of igneous rocks and are used in rock classification. There are six main types of textures; phaneritic, aphanitic, porphyritic, glassy, pyroclastic and pegmatitic.
What texture is igneous rocks?
The texture of an igneous rock made up entirely of crystals big enough to be easily seen with the naked eye is phaneritic. Phaneritic texture is sometimes referred to as coarse-grained igneous texture. Granite, the most well known example of an intrusive igneous rock, has a phaneritic texture.
What are the types of igneous rocks based on texture?
There are nine main types of igneous rock textures: Phaneritic, vesicular, aphanitic, porphyritic, poikilitic, glassy, pyroclastic, equigranular, and spinifex. Each kind of texture has a variety of different characteristics that make them unique.
What are the 3 classification of igneous rocks?
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 you do Iugs classification?
The principles are: (1) use descriptive attributes; (2) use actual properties; (3) ensure suitability for all geologists; (4) use current terminology; (5) define boundaries of rock species; (6) keep it simple to apply; (7) follow natural relations; (8) use modal mineralogy; (9) if mode not feasible, use chemistry; (10) …
When did IUGS start classification of igneous rocks?
In 1976, a subcommission of the International Union of Geological Sciences ( IUGS) proposed a classification scheme for plutonic and volcanic igneous rocks. As with most classification systems, this proposal sought to standardize the language spoken by petrologists, as many systems for naming igneous rocks were in limited, regional use at the time.
When did they start naming plutonic igneous rocks?
An international effort to systematize the nomenclature of plutonic igneous rocks was started in the 1960s under the leadership of Swiss petrologist Albert Streckeisen, and summaries of this work (e.g., Streckeisen, 1974, 1976; LeBas and Streckeisen, 1991) are the standard references for current nomenclature.
Why are igneous rocks so difficult to classify?
General Classification of Igneous Rocks Classification of igneous rocks is one of the most confusing aspects of geology. This is partly due to historical reasons, partly due to the nature of magmas, and partly due to the various criteria that could potentially be used to classify rocks.
What kind of apices do gabbroic rocks have?
Gabbroic rocks can be classified using a tetrahedron with apices of plagioclase, olivine, orthopyroxene, and clinopyroxene (POOC; Fig. 8).