Other specimens - Click the thumbnails to enlarge. Introduction Features Igneous rocks Sedimentary rocks Metamorphic rocks. Introduction Features Igneous rocks Sedimentary rocks Metamorphic rocks Quartzite Quartzite is a metamorphic rock formed when quartz-rich sandstone or chert has been exposed to high temperatures and pressures. Left- Slate fragments resulting from rock cleavage.
Right- The same rock type in outcrop. Left- A hand sample showing a satin texture. Right- The same rock type in outcrop in the city of Sopron, Hungary. Top- Hand sample showing light reflecting off of mica crystals. Bottom- Close-up view of mica crystals and garnet. Photos by R. Click the image for photo sources and terms of use. Gneiss Gneiss Figure Top- Hand samples showing that colour bands can be continuous left or less so right. Bottom- Gneiss in outcrop at Belteviga Bay, Norway.
Notice the light and dark stripes on the rock. Click the image for more attributions. Green crystals are the amphibole hornblende, and colourless crystals are plagioclase feldspar. Note horizontal crystal alignment. Source: D. Click the image for original figure caption and terms of use. Types of Non-foliated Metamorphic Rocks Metamorphic rocks that form under low-pressure conditions or under the effects confining pressure, which is equal in all directions, do not become foliated.
Marble Marble Figure Left- Marble made of pure calcite is white. Upper right- microscope view of calcite crystals within marble that are blocky and not aligned. Quartzite Quartzite Figure Left- Quartzite from the Baraboo Range, Wisconsin. Right- Photomicrograph showing quartz grains in quartzite from the Southern Appalachians. In the upper left half of the image, blocky quartz crystals show some evidence of alignment running from the upper right to the lower left.
Hornfels Hornfels is another non-foliated metamorphic rock that normally forms during contact metamorphism of fine-grained rocks like mudstone or volcanic rocks. Left- Hornfels from the Novosibirsk region of Russia from a sedimentary protolith. Dark and light bands preserve the bedding of the original sedimentary rock.
The rock has been recrystallized during contact metamorphism and does not display foliation. Right- Hornfels in thin section from a sedimentary protolith. Note that the brown mica crystals are not aligned. The dark band at the top reflects the layering within the sedimentary parent rock, similar to the way those layers are preserved in the sample on the left. Click the image for terms of use. Click the table for a text version.
Migmatite: Both Metamorphic and Igneous If a metamorphic rock is heated enough, it can begin to undergo partial melting in the same way that igneous rocks do. Ptygmatic folding happens when a stiff layer within a rock is surrounded by weaker layers. Folding causes the stiff layer to crinkle while the weaker layers deform around it. Which metamorphic rock is described in each of the following? There are three types of foliated rocks: slate , schist, and gneiss. Each type varies based on the size of the mineral grain and how foliation is characterized.
Gneiss can be formed from a sedimentary rock such as sandstone or shale, or it can be formed from the metamorphism of the igneouse rock grantite. The best way to tell quartzite from sandstone is to break the rocks.
Sandstone will shatter into many individual grains of sand while quartzite will break across the grains. There are three ways that metamorphic rocks can form. The three types of metamorphism are Contact, Regional, and Dynamic metamorphism. Contact Metamorphism occurs when magma comes in contact with an already existing body of rock.
There are two main mechanisms of metamorphism , heat and pressure. HEAT : There are two sources of heat , one comes from the geothermal gradient - the increase in temperature that occurs with increase in depth in the earth. Sandstone is a rock comprising mostly of minerals formed from sand. The stone gains its formation throughout centuries of deposits forming in lakes, rivers, or on the ocean floor.
These elements group together with the minerals quartz or calcite and compresses. Gneiss is a foliated metamorphic rock that has a banded appearance and is made up of granular mineral grains. It typically contains abundant quartz or feldspar minerals. Slate is a fine-grained, foliated metamorphic rock that is created by the alteration of shale or mudstone by low-grade regional metamorphism. Uses of gneiss The minerals in gneiss do not etch when exposed to normal household acids like vinegar or citrus.
Take comfort in knowing that gneiss can withstand heavy use; it is made up of minerals in the range on Mohs scale, meaning it's harder than glass and about the same hardness as steel. Ornamental Stone Metamorphic Gneiss has many uses as a building material such as flooring, ornamental stones, gravestones, facing stones on buildings and work surfaces.
Gneiss is a high grade metamorphic rock, meaning that it has been subjected to higher temperatures and pressures than schist. It is formed by the metamorphosis of granite, or sedimentary rock. Gneiss displays distinct foliation, representing alternating layers composed of different minerals. 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. When gneiss is melted , it crystallizes into igneous rock.
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