Do metamorphic rocks have bands of light and dark colors?
Dark bands are largely amphibole while the light-colored bands are feldspar and quartz. Most gneiss has little or no mica because it forms at temperatures higher than those under which micas are stable. Figure 6.17 Gneiss, a coarse-grained, high grade metamorphic rock, is characterized by color bands.
Why do metamorphic rocks have different colors?
Deep inside the Earth, intense heat and pressure can change rocks into entirely new metamorphic rocks. In fact, the conditions are so extreme, they can change the rock's texture, color, and the shape of its crystals. Even the rock's minerals are broken down and new ones are formed.
What metamorphic rocks have bands of color?
Figure 10.17 Gneiss, a coarse-grained, high grade metamorphic rock, is characterized by colour bands.
Why does metamorphic rocks have bands?
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 causes wavy bands of light and dark minerals?
The correct answer is (4) heat and pressure during metamorphism. The narrow bands in a metamorphic rock are formed when the minerals are realigned due to the presence of high temperature and pressure.
Why does gneiss have light and dark bands?
The alternating darker and lighter bands in Gneiss are because of mafic and felsic minerals therein. It happens that the heat had affected both minerals light and dark as we knew that before as it was a granite with light coloured minerals such as feldspars, quartz and micas.
What causes igneous rocks to be dark colored?
Mafic refers to igneous rocks with an abundance of ferromagnesian minerals (those with the elements Mg and Fe in their chemical formulae) plus plagioclase feldspar. Such minerals are dark-colored and include pyroxene and olivine .
Why are some igneous rocks darker in color and others lighter in color?
The different elements present in the different igneous compositions will form different minerals. Rocks with high amounts of iron (Fe) tend to form minerals that are dark in color (such as olivine and pyroxene). As result mafic rocks tend to be dark in color and felsic rocks tend to be lighter in color.
What is a foliated metamorphic rock with dark and light minerals?
One type is described as a layering of dark and light-colored minerals so that the foliation is defined as alternating dark and light mineral bands throughout the rock. Such a foliation is called gneissic banding (Figure 11.3), and the metamorphic rock is called gneiss (pronounced “nice”, with a silent g).
When a metamorphic rock exhibits a layered or banded appearance?
Cards
| Term Rocks are aggregates of one of more minerals. T or F | Definition True |
|---|---|
| Term When a metamorphic rock exhibits a layered or banded appearance it is said to exhibit a ____________ texture | Definition foliated |
| Term The rock produced by the metamorphism of limestone is | Definition marble |
•Sep 20, 2009
How does mineral changes in metamorphic rocks?
During metamorphism, new minerals grow, with different sizes, shapes, and orientations than those of the original minerals. The chemical composition of the original rock may also change, as some elements are carried away and others are added by the fluids flowing through the rocks.
What features best describe metamorphic rocks?
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 banding in metamorphic rocks?
Banding means that the rock consists of alternating, thin layers (typically 1 mm to 1 cm) of two different mineral compositions. Normally, the two types of layers have the same kinds of minerals, but in different proportions, giving the rock a striped appearance.
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.
What minerals make up the light and dark bands in gneiss?
Mineralogy – felsic minerals such as feldspar ( orthoclase, plagioclase) and quartz generally form the light coloured bands; mafic minerals such as biotite, pyroxene ( augite) and amphibole ( hornblende) generally form the dark coloured bands; garnet porphyroblasts common.
How do light colored igneous rocks differ from dark-colored rocks?
Light-colored igneous rocks are more granitic (felsic) in composition and contain more feldspar and silica. Dark-colored igneous rocks are more basaltic (mafic) in composition and contain more iron and magnesium.
What are the dark colored rocks and the light colored rocks?
Felsic minerals (quartz, K feldspar, etc) are light colored while mafic minerals (hornblende, pyroxenes) are normally dark colored. Felsic minerals have the lowest melting points (600 to 750 °C) and mafic minerals have higher melting points (1000 to 1200 °C).
What causes the different colors in igneous rocks?
The rocks have different colors because of different mineral compositions. Light-colored, white, or yellow rocks can be composed mostly of quartz, plagioclase, or calcite. Dark-colored, black, rocks can be made of pyroxene, biotite, or chromite. The red color of the rock is explained by iron oxides.
Why are some metamorphic rocks foliated and others not?
There are two main types of metamorphic rocks: those that are foliated because they have formed in an environment with either directed pressure or shear stress, and those that are not foliated because they have formed in an environment without directed pressure or relatively near the surface with very little pressure …
What is composed of alternating bands of light and dark minerals?
One type is described as a layering of dark and light-colored minerals so that the foliation is defined as alternating dark and light mineral bands throughout the rock. Such a foliation is called gneissic banding (Figure 11.3), and the metamorphic rock is called gneiss (pronounced “nice”, with a silent g).
Why do bands of minerals develop in most metamorphic rocks?
Heat and pressure can break bonds in minerals, and the atoms can then join in new ways to make new minerals. Why do bands of minerals grow within existing rocks? Because most rocks contain several types of minerals.
What happens to minerals during metamorphism?
Metamorphism occurs because some minerals are stable only under certain conditions of pressure and temperature. When pressure and temperature change, chemical reactions occur to cause the minerals in the rock to change to an assemblage that is stable at the new pressure and temperature conditions.
Which may be characteristics displayed by metamorphic rocks?
Describe some characteristics displayed by metamorphic rocks and shear zones. small ridges, schist, cleavage, foliation and layers.
What is the most obvious characteristic of a metamorphic rock?
The most obvious features of metamorphic rocks are certain planar features that are often termed s-surfaces. The simplest planar features may be primary bedding (akin to the layering in sedimentary rocks).
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.
What makes a mineral dark or light?
Broadly speaking, mineral colour indicates the specific gravity of the mineral; minerals that are lighter in colour are also lighter in weight. Darker minerals typically contain more of the relatively heavy elements, notably iron, magnesium, and calcium.
What makes a mineral dark or light and where are they formed?
The most common minerals produced by high temperature magma include olivine, pyroxene, amphibole, and plagioclase. These minerals are usually dark colored, ranging from black to dark greens and grays, and they produce dark colored rocks.
Why are minerals different colors?
Minerals are colored because certain wavelengths of incident light are absorbed, and the color we perceive is produced by the remaining wavelengths that were not absorbed. Some minerals are colorless.
How are foliated metamorphic rocks different from non-foliated metamorphic rocks?
Foliated metamorphic rocks exhibit layers or stripes caused by the elongation and alignment of minerals in the rock as it undergoes metamorphism. In contrast, nonfoliated metamorphic rocks do not contain minerals that align during metamorphism and do not appear layered.
How does a metamorphic rock change into another type of metamorphic rock?
Explanation: Metamorphic rocks are formed by tremendous heat, great pressure, and chemical reactions. To change it into another type of metamorphic rock you have to reheat it and bury it deeper again beneath the Earth's surface.