What type of metamorphic rock has a banded appearance?
Foliated metamorphic rocks such as gneiss, phyllite, schist and slate have a layered or banded appearance that is produced by exposure to heat and directed pressure.
What happens when minerals become banded in a metamorphic rock?
Gneiss As metamorphic grade increases, the sheet silicates become unstable and dark colored minerals like hornblende and pyroxene start to grow. These dark colored minerals tend to become segregated in distinct bands through the rock, giving the rock a gneissic banding.
What is the most common characteristic of metamorphic rocks in which the rocks have a banded appearance?
Metamorphic rocks were once igneous or sedimentary rocks, but have been changed (metamorphosed) as a result of intense heat and/or pressure within the Earth's crust. They are crystalline and often have a “squashed” (foliated or banded) texture.
What is a banded metamorphic rock?
« Back to Glossary Index. A separation of light (felsic) and dark (mafic) minerals in higher grade metamorphic rocks like gneiss.
What causes banding in metamorphic rocks?
The banding is usually due to the presence of differing proportions of minerals in the various bands; dark and light bands may alternate because of the separation of mafic (dark) and felsic (light) minerals. Banding can also be caused by differing grain sizes of the same minerals.
What type of metamorphism do not have a layered or banded appearance?
Non-foliated metamorphic rocks do not have a layered or banded appearance. Examples of nonfoliated rocks include: hornfels, marble, novaculite, quartzite, and skarn.
Which type of pressure will result in the alignment of metamorphic minerals?
The metamorphic process can occur at almost any pressure, from near surface pressure (for contact metamorphism) to pressures in excess of 16 kbar (1500 Mpa).
Why are metamorphic rocks often banded or layered?
Foliated Metamorphic Rocks: Foliation forms when pressure squeezes the flat or elongate minerals within a rock so they become aligned. These rocks develop a platy or sheet-like structure that reflects the direction that pressure was applied.
What is mineral alignment?
Minerals can become aligned due to the circumstances of their environment. The process has been given the name foliation to describe when minerals become aligned.
What causes compositional banding?
However, compositional banding can be the result of nucleation processes which cause chemical and mineralogical differentiation into bands. This typically follows the same principle as mica growth, perpendicular to the principal stress.
How are foliated metamorphic rocks identified?
Foliated metamorphic rocks: Grain size is the main basis for classification of foliated metamorphic rocks. Schists are coarser grained and well-foliated; individual grains are large enough to identify without a microscope. The foliation in schists may be wavy or crinkled. Mica is commonly a prominent mineral in schist.
How are foliated metamorphic rocks formed?
Foliated Metamorphic Rocks: Foliation forms when pressure squeezes the flat or elongate minerals within a rock so they become aligned. These rocks develop a platy or sheet-like structure that reflects the direction that pressure was applied.
Which rock is foliated shows mineral alignment?
Slate, for example, is characterized by aligned flakes of mica that are too small to see. The various types of foliated metamorphic rocks, listed in order of the grade or intensity of metamorphism and the type of foliation are slate, phyllite, schist, and gneiss (Figure 7.8).
How metamorphic rocks are formed?
The conditions required to form a metamorphic rock are very specific. The existing rock must be exposed to high heat, high pressure, or to a hot, mineral-rich fluid. Usually, all three of these circumstances are met.
What causes banding in metamorphic rock?
The banding is usually due to the presence of differing proportions of minerals in the various bands; dark and light bands may alternate because of the separation of mafic (dark) and felsic (light) minerals. Banding can also be caused by differing grain sizes of the same minerals.
Why metamorphic rocks are foliated?
Foliated Metamorphic Rocks As pressure squeezes on a parent rock during recrystallization it causes the platy or elongated minerals within the rock to become aligned, or foliated. Foliated rocks develop a platy or sheet-like structure that reflects the direction that pressure was applied in.
What causes banding in rocks?
The banding is usually due to the presence of differing proportions of minerals in the various bands; dark and light bands may alternate because of the separation of mafic (dark) and felsic (light) minerals. Banding can also be caused by differing grain sizes of the same minerals.
Are metamorphic rocks foliated?
Foliated Metamorphic Rocks: Some kinds of metamorphic rocks — granite gneiss and biotite schist are two examples — are strongly banded or foliated. (Foliated means the parallel arrangement of certain mineral grains that gives the rock a striped appearance.)
How is a metamorphic rock formed quizlet?
Metamorphic rocks are formed by intense heat, intense pressure, or by the action of watery hot fluids (metamorphism).
How are rocks formed from minerals?
Through the process of erosion, these fragments are removed from their source and transported by wind, water, ice, or biological activity to a new location. Once the sediment settles somewhere, and enough of it collects, the lowest layers become compacted so tightly that they form solid rock.
What is required for a metamorphic rock to be banded?
Foliated Metamorphic Rocks: (Foliated means the parallel arrangement of certain mineral grains that gives the rock a striped appearance.) Foliation forms when pressure squeezes the flat or elongate minerals within a rock so they become aligned.
How are metamorphic rocks formed?
Metamorphic rocks form when rocks are subjected to high heat, high pressure, hot mineral-rich fluids or, more commonly, some combination of these factors. Conditions like these are found deep within the Earth or where tectonic plates meet.
What is a metamorphic rock quizlet?
Metamorphic Rock. any rock that has been changed physically and or chemically by forces of intense heat and pressure.
How do minerals combine to form a metamorphic rock?
Metamorphic rocks form when an existing rock is changed by heat or pressure. The minerals in the rock change but do not melt (Figure below). The rock experiences these changes within the Earth.
What is a banded rock called?
gneiss, metamorphic rock that has a distinct banding, which is apparent in hand specimen or on a microscopic scale.
What minerals are in metamorphic rocks?
Common minerals in metamorphic rocks include quartz, feldspar, mica, calcite, and hornblende. Index minerals in metamorphic rocks indicate how much the original rock was metamorphosed, called the grade of metamorphism. Index Minerals minerals include chlorite, epidote, garnet, staurolite, kyanite and sillimanite.
How are minerals formed in metamorphic rock?
New minerals are created either by rearrangement of mineral components or by reactions with fluids that enter the rocks. Pressure or temperature can even change previously metamorphosed rocks into new types. Metamorphic rocks are often squished, smeared out, and folded.
How are the metamorphic rocks formed?
The conditions required to form a metamorphic rock are very specific. The existing rock must be exposed to high heat, high pressure, or to a hot, mineral-rich fluid. Usually, all three of these circumstances are met.