unit 6 - rocks and minerals

Metamorphic rocks are classified based on foliation as foliated rocks and non-foliated rocks. Foliation means the existence of series of parallel surface. These rocks usually contain crystal.

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gneiss-metamorphic

Gneiss is foliated metamorphic rock that has a banded appearance and is made up of granular mineral grains. It typically contains abundant quartz or feldspar minerals.

Granite - igneous rock

Granite is a light-colored igneous rock with grains large enough to be visible with the unaided eye. It forms from the slow crystallization of magma below Earth's surface. Granite is composed mainly of quartz and feldspar with minor amounts of micas, amphiboles and other minerals. This mineral composition usually gives granite a red, pink, gray or white color with dark mineral grains visible throughout the rock.

Igneous Rocks

IGNEOUS ROCKS Andesite Basalt Diorite Gabbro Granite Obsidian Peridotite Pumice Rhyolite Scoria Tuff

Metamorphic Rocks

METAMORPHIC ROCKS Amphibolite Gneiss Hornfels Marble Phyllite Quartzite Schist Slate

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SEDIMENTARY ROCKS Breccia Chert Coal Conglomerate Iron Ore Limestone Rock Salt Sandstone Shale Siltstone

amphiboite - metamorphic

What is Amphibolite? Amphibolite is a non-foliated metamorphic rock that forms through recrystallization under conditions of high viscosity and directed pressure. It is composed primarily of amphibole and plagioclase, usually with very little quartz.

slate - metamorphic

What is Slate? Slate is a fine-grained, foliated metamorphic rock that is created by the alteration of shale or mudstone by low-grade regional metamorphism. It is popular for a wide variety of uses such as roofing, flooring and flagging because of its durability and attractive appearance. Composition of Slate Slate is composed mainly of clay minerals or micas depending upon the degree of metamorphism to which it has been subjected. The original clay minerals in shale alter to micas with increasing levels of heat and pressure. Slate can also contain abundant quartz and small amounts of feldspar, calcite, pyrite, hematite and other minerals. Color of Slate Most slates are gray in color and range in a continuum of shades from light to dark gray. Slate also occurs in shades of green, red, black, purple and brown. The color of slate is often determined by the amount and type of iron and organic material that are present in the rock. How Does Slate Form? The tectonic environment for producing slate is usually a former sedimentary basin that becomes involved in a convergent plate boundary. Shales and mudstones in that basin are compressed by horizontal forces with minor heating. These forces and heat modify the clay minerals in the shale and mudstone. Foliation develops at right angles to the compressive forces of the convergent plate boundary to yield a vertical foliation that usually crosses the bedding planes that existed in the shale. Uses of the Word "Slate" The word "slate" has not been used consistently over time and in some industries. Today most geologists are careful not to use the word "slate" when talking about "shale". However, in the past the word slate was often used freely in reference for shale. This confusion of terms partially arises from the fact that shale is progressively converted into slate. Imagine driving your car eastwards in Pennsylvania through areas of increasing metamorphism, starting where the rock is definitely "shale" and stopping to examine rock at each outcrop. You will have a difficult time deciding where on that route "shale" has been converted into "slate". It can be difficult to pick up a rock and apply the proper name where the rocks have been lightly metamorphosed. In the coal mining industry of the Appalachian Basin, the word "slate" is still used by many miners to in reference to the shale that forms the roof and floor of a mine and for fragments of shale that are separated from the coal in preparation plants. Experienced miners train newer miners and archaic language is passed along. Slaty Cleavage Foliation in slate is caused by the parallel orientation of platy minerals in the rock such as microscopic grains of clay minerals and mica. These parallel mineral grain alignments give the rock an ability to break smoothly along planes of foliation. People exploit this property of slate to produce thin sheets of slate that are used in construction projects and manufacturing.

Metamorphic rocks

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Marble - metamorphic

What is Marble? Marble is a non-foliated metamorphic rock that is produced from the metamorphism of limestone. It is composed primarily of calcium carbonate.

basalt - igneous rock

.What is Basalt? Basalt is a dark-colored, fine-grained, igneous rock composed mainly of plagioclase and pyroxene minerals. It most commonly forms as an extrusive rock, such as a lava flow, but can also form in small intrusive bodies, such as an igneous dike or a thin sill. It has a composition similar to gabbro. The difference between basalt and gabbro is that basalt is a fine-grained rock while gabbro is a coarse-grained rock.

Igneous Rocks

Igneous rocks are the oldest type of rocks on the earth. All the other types of rocks are formed from igneous rocks. Igneous rocks are formed when magma (molten materials) rise from the earth's interior. Igneous rocks can be sub classified further according to their depth of formation. The rocks that form below the earth surface are called as intrusive igneous rocks, and rocks that form on the earth surface are called extrusive igneous rocks (volcanic rocks). These rocks contain silica 40% to 80%. Magnesium and iron are important among others. Granite, pegmatite, gabbro, dolerite, and basalt are some examples for igneous rocks. Read more: http://www.differencebetween.com/difference-between-igneous-rocks-and-vs-metamorphic-rocks/#ixzz1ryY64O4i

Metamorphic Rocks

Metamorphic rocks are formed due to metamorphism from existing igneous or sedimentary rocks, or even from existing metamorphic rocks. When existing rocks undergo changes due to high pressure and/or high temperature and/or high shearing stresses, metamorphic rocks are formed. Usually metamorphic rocks are formed deep in the earth. Heat comes from magma, while pressure comes from the layer of rocks on top of the other layers. Metamorphic rocks are classified based on foliation as foliated rocks and non-foliated rocks. Foliation means the existence of series of parallel surface. These rocks usually contain crystal. Gneiss, slate, marble, and quartzite are some of the metamorphic rocks.

Breccia - sedementary

What is Breccia? Breccia is a term most often used for clastic sedimentary rocks that are composed of large angular fragments (over two millimeters in diameter). The spaces between the large angular fragments can be filled with a matrix of smaller particles or a mineral cement that binds the rock together. How Does Breccia Form? Breccia forms where broken, angular fragments of rock or mineral debris accumulate. One possible location for breccia formation is at the base of an outcrop where mechanical weathering debris accumulates. Another would be in stream deposits near the outcrop such as an alluvial fan. Some breccias form as debris flow deposits. The angular particle shape reveals that they have not been transported very far (transport wears the sharp points and edges of angular particles into rounded shapes). After deposition the fragments are bound together by a mineral cement or by a matrix of smaller particles that fills the spaces between the fragments. How Does Breccia Differ From Conglomerate? Brccia and conglomerate are very similar rocks. They are both clastic sedimentary rocks composed of particles larger than two millimeters in diameter. The difference is in the shape of the large particles. In breccia the large particles are angular in shape but in conglomerate the particles are rounded. This reveals a difference in how far the particles were transported. Near the outcrop where the fragments were produced by mechanical weathering the shape is angular. However, during transport by water away from the outcrop the sharp points and edges of those angular fragments are rounded. The rounded particles would form a conglomerate. What is Breccia's Composition? Breccia has many compositions. Its composition is mainly determined by the rock and mineral material that the angular fragments were produced from. The climate of the source area can also influence composition. Most breccias are a mix of rock fragments and mineral grains. The type of rock that the fragments were produced from is often used as an adjective when referring to the rock. Some examples: sandstone breccia, limestone breccia, granite breccia, chert breccia, basalt breccia and others. Often a breccia will contain many types of angular rock fragments. These are known as polymict breccias or polymictic breccias.

Gabbro - igneous

What is Gabbro? Gabbro is a coarse-grained, dark-colored, intrusive igneous rock. It is usually black or dark green in color and composed mainly of the minerals plagioclase and augite. It is the most abundant rock in the deep oceanic crust. What Minerals are in Gabbro? Gabbro is composed mainly of calcium-rich plagioclase feldspar (usually labradorite or bytownite) and clinopyroxene (augite). Minor amounts of olivine and orthopyroxene might also be present in the rock. (see composition chart at right) This mineral composition usually gives gabbro a black to very dark green color. A minor amount of light-colored mineral grains may be present. Unlike many other igneous rocks, gabbro usually contains very little quartz. (see a close-up view of gabbro at right) Gabbro and Basalt are Related Gabbros are equivalent in composition to basalts. The difference between the two rocks is their grain size. Basalts are extrusive igneous rocks that cool quickly and have fine-grained crystals, while gabbros are intrusive igneous rocks that cool slowly and have coarse-grained crystals. Gabbro in Oceanic Crust It is often stated that Earth's oceanic crust is made-up of basalt. The word "basalt" is used because the rocks of the oceanic crust have a "basaltic" composition. However, a thin surface veneer of oceanic crust is basalt and the deeper rocks are generally coarser-grained gabbro. These differential rates of cooling occur at divergent plate boundaries in oceanic lithosphere. (see illustration at right). Gabbro in Continental Crust On the continents, gabbro can be found within thick lava flows where slow cooling allows large crystals to form. Gabbro will also be present in the deep plutons that form when magma chambers that feed basaltic eruptions crystallize. Uses of Gabbro Gabbro can be polished to a brilliant black luster. Brightly polish gabbro is used to make cemetery markers, kitchen counter tops, floor tiles, facing stone and other dimension stone products. It is a highly desirable rock that stands up to weathering and wear. In the dimension stone industry gabbro is sold under the name "black granite". Gabbro is also used to make a number of rough-cut products such as curbing, ashlars, paving stones and other products. Gabbro as an Ore Gabbro often contains economic amounts of some relatively rare metals. Gabbros containing significant amounts of the mineral ilmenite are mined for their titanium content. Other gabbros are mined to yield nickel, chromium or platinum.

Obsidian

What is Obsidian? Obsidian is an igneous rock that forms when molten rock material cools so rapidly that atoms are unable to arrange themselves into a crystalline structure. The result is a volcanic glass with a smooth uniform texture that breaks with a conchoidal fracture (see photo on right). Where Does Obsidian Form? Obsidian is usually an extrusive rock - one that solidifies above Earth's surface. However, it can form in a variety of cooling environments: •along the edges of a lava flow (extrusive) •around the edges of a sill or a dike (intrusive) •where lava contacs water (extrusive) •where lava cools while airborne (extrusive) What Color is Obsidian? Black is the most common color of obsidian. However, it can also be brown or green. Rarely, obsidian can be blue, red, orange or yellow. The colors are thought to be caused mainly by trace elements or inclusions. Occasionally two colors of obsidian will be swirled together in a single specimen. The most common color combination is black and brown obsidian swirled together - that's called "mahogany obsidian" (see photo). As a "glass", obsidian is chemically unstable. With the passage of time, some obsidian begins to crystallize. This process does not happen at a uniform rate throughout the rock. Instead it begins at various locations within the rock. At these locations the crystallization process forms radial clusters of white or gray cristobalite crystals within the obsidian. When cut and polished these specimens are referred to as "snowflake obsidian" (see photos at right).

Pumice - igneous

What is Pumice? Pumice is a light-colored vesicular igneous rock. It forms through very rapid solidification of a melt. The vesicular texture is a result of gas trapped in the melt at the time of solidification.

qartzite- metamorphic

What is Quartzite? Quartzite is a non-foliated metamorphic rock that is produced by the metamorphism of sandstone. It is composed primarily of quartz.

Rhyolite -igneous

What is Rhyolite? Rhyolite is a light-colored, fine-grained, extrusive igneous rock that typically contains quartz and feldspar minerals.

schist -metamorphic

What is Schist? Schist is metamorphic rock with well developed foliation. It often contains significant amounts of mica which allow the rock to split into thin pieces. It is a rock of intermediate metamorphic grade between phyllite and gneiss.

Scoria - igneous

What is Scoria? Scoria is a dark-colored, vesicular, extrusive igneous rock. The vesicles are a result of trapped gas within the melt at the time of solidification. It often forms as a frothy crust on the top of a lava flow or as material ejected from a volcanic vent and solidifying while airborne.