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Igneous rocks are generally classified first on the basis of theirformation (and therefore their texture) as intrusive or extrusive.Intrusive rocks are solidified from magma u…nder the surfaceresulting in a visible crystalline texture, and extrusive igneousrocks are solidified from lava at or near the surface, resulting ina small or nearly invisible crystalline texture. Igneous rock can additionally be classified by general chemistrycomposition as felsic, intermediate, mafic, and ultramafic. Felsicrocks are higher in silica and aluminum. Mafic rocks are higher inmagnesium and iron.
Look at them. There shape, size, color and feel! Dont worry you will figure it out....
where they were formed
Igneous rocks are classified by their mineral composition and texture.
Geologists classify rocks by where they are formed; above ground or under ground
Igneous rocks The term igneous comes from the Latin ignis, meaning "fire". Igneous is used to describe rocks that crystallize out of hot molten material in the Earth called …magma. When magma pushes up through Earth's crust to the surface, it is called lava. Both magma and lava cool and harden to form igneous rocks. Intrusive vs. Extrusive Igneous rocks can be classified into two main categories: intrusive and extrusive. A trick to help kids remember intrusive and extrusive is to think of intrusive -- inside and extrusive -- exit. Granite. Intrusive rocks come from magma. They cool slowly deep in Earth's crust. When magma cools underground, the crust acts like a blanket, insulating it, keeping it warm longer. Because the magma cools slowly, crystals of different minerals have time to grow. The molecules in the magma have time to arrange themselves into crystal formations before the magma hardens. Intrusive rocks have large crystals that can be seen with the naked eye. A common example of an intrusive igneous rock is granite. Pahoehoe Lava Field, Hawaii. Extrusive igneous rocks come from lava. Lava, at the surface, is exposed to air and water which causes the molten rock to cool rapidly. Solidifying rocks at the surface cool too quickly for large crystals to form. Molecules in the lava do not have time to arrange themselves to form large crystals. Extrusive rocks have crystals that are too small to see without magnification. A common example of an extrusive igneous rock is basalt. Some extrusive rocks, such as obsidian and pumice, cool so rapidly that they completely lack crystal structure and are considered a volcanic glass. Pumice is just like obsidian except it is tiny shards of glass. Texture Within the two main categories of intrusive and extrusive, rock can be classified even further using texture and chemical composition. The word "texture" has nothing to do with how the rock feels. Texture, in geology, is used to describe how the rock looks. The most noticeable textural feature of igneous rocks is grain size. Grain size refers to the size of the individual mineral crystals. As mentioned above, intrusive igneous rocks, such as granite have large, individual crystals visible to the naked eye. The textural term used to describe a rock with large crystals is coarse-grained. In contrast, fine-grained rocks, such as basalt, are igneous rocks that have crystals too fine to see with the naked eye. Under magnification they are still very small but easily identifiable with a few optic tests. Quickly-cooled lavas can contain trapped bubbles of gas, which are called vesicles. The resulting texture is described as vesicular. Chemical Composition Chemical composition of igneous rock can often be estimated just from looking at the rock. Geologists look at the proportions of light-colored and dark-colored minerals in an igneous rock to estimate the chemical makeup of rock. Light-colored or felsic, minerals have more silica in them. Silica is one of the most abundant elements on Earth and is the chief component of quartz. Felsic minerals are most often colorless, white, gray or pink but can be any number of colors. The dark, or mafic, minerals are richer in iron and magnesium. Mafic minerals are chiefly black, brown, dark gray and sometimes green. The mineral proportions of the rock are what allows geologists to classify rocks chemically. Depending on the proportion of light minerals to dark minerals, igneous rocks can be broken into four main types: felsic, intermediate, mafic and ultramafic. The following list gives more information about igneous chemical categories. Felsic rocks are high in silica (65% +). They are usually light-colored. Some examples are: Rhyolite (extrusive) and granite (intrusive). Intermediate rocks have lower silica content (55-65%). They are darker than felsic rocks but lighter than mafic rocks. Some examples are: Andesite/dacite (extrusive) and diorite/granodiorite (intrusive). Mafic rocks have low silica content (45-55%). They are usually dark-colored and contain iron and magnesium. Some examples are: Basalt (extrusive) and gabbro (intrusive). Basalt is the rock that is produced at spreading ridges and makes up the sea floor. Ultramafic rocks have extremely low silica content (less than 45%) and contain large amounts of iron and magnesium. They are usually dark-colored, but high olivine content can lend green shades to the rock. Other rare colors can be found. An example of ultramafic rock is Peridotite (intrusive).
Their texture and mineralogy.
There are two types of igneous rocks; intrusive and extrusive. Intrusive igneous rocks are formed underneath the earth's surface from magma where it cools slower and develops …large crystal structures. Extrusive igneous rocks are formed above the earth's surface from lava that cools quickly and creates rocks with smaller, finer crystal structures.
Formed by gaseous fire
Igneous rocks are formed by the cooling of lava (above Earth's surface) or magma (below). Rocks in general are classified by their mineral composition, texture, and origin. Ig…neous rocks all have the origin of molten material, there are two categories within this: intrusive and extrusive. Intrusive rocks formed below earth's surface and extrusive rocks above. Their mineral composition varies greatly and depends on each individual rock. The classification of igneous rocks in texture is linked to their origin. The texture of a rock is defined by its grain: can you see and feel the little rocks that make it up? If you can, that rock has a coarse grain, if you can't see the bits, it is fine grained. Intrusive igneous rocks are usually fine grained; extrusive, coarse grained.
igenous rock can classified into to extrusive and intrusive.
They are rocks formed from magma that cools and crystallizes on the earth surface.
Basalt is considered igneous because it forms when mafic lava cools at Earth's surface.
Igneous Rocks by Composition. Igneous rocks are classified according to their mineral content: Ultramafic rocks are dominated by olivine and/or pyroxene.
PYROCLASTIC ROCKS AND TEPHRA, Pyroclasts .
No, sandstone is a sedimentary rock.
In Igneous Rock
Intrusive and Extrusive.