all about rocks

7/29/2019 ALL ABOUT ROCKS

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Igneous Rocks

"Igneous" comes from the Latin word for fire, and refers to rocks that

formed from molten material. Igneous rocks can be extrusive or

intrusive. They are classified based on their texture and composition.

Topics:

1.Extrusiveand intrusive

2.Classification

3.Common igneous rocks

Extrusive and Intrusive (Part 1)

Extrusive Rocks

Extrusiveigneous rocks form on the earths surface.

Lava flows form from volcanic eruptions.

Pahoehoe lava flow (Photograph by Parvinder Sethi)
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Glowing lava (Photograph by Parvinder Sethi)

Lava flows are a type of extrusive igneous rock. This lava, fromHawaii, is called pahoehoe because of its smooth, shiny, ropy

texture.

Extrusive Rocks (Continued)

Pyroclasticrocks form from the lithification of broken fragments ofrock from volcanic eruptions.

Pyroclastic texture in a volcanic breccia (Photograph by Parvinder Sethi)


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This rock is made up of broken pieces of volcanic material. It is called

a volcanic breccia, and is a type of extrusive igneous rock.

Flood basalts are very large lava flows that come from large

fissures or cracks in the earth.

CatoctinFormation, an ancient flood basalt in Virginia (Photograph by Stan Johnson)

The Catoctin Formation, shown here along the Blue Ridge Parkway, isan ancient flood basalt. This basalt flowed over large parts of Virginia

about 570 million years ago.

Intrusive Rocks

Intrusiveigneous rocks form below the earths surface. They are

classified based on their shapes and relationships to the pre-existing orhost rock.

Adike is a tabular mass that cuts across surrounding rocks.

A sill is a tabular mass that is parallel to planar structures (such as

layers) in surrounding rocks.

Abatholith is a large body of irregular shape that cuts across

surrounding rocks. Batholiths are commonly composed of granite.


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Astockis like a batholith, but smaller.

Intrusions (Diagram by Roy Sites)

This diagram shows the different kinds of igneous intrusions. Notethat the dike, batholith, and stock cut across the layers whereas the

sill is parallel to the layers.

Classification

The classification of igneous rocks is based on texture andcomposition. Texture is the description of the size, shape, and

arrangement of the mineral grains in a rock. Composition refers to

the types of minerals that make up the rock.

Texture (Part 1)

Texture is determined mainly by the cooling rate of magma.

Slow cooling occurs deep within the earth, and produces

aphaneritictexture. Phaneritic means that mineral grains are largeenough to be seen with the naked eye.


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Phaneritic texture in diorite (Photograph by Parvinder Sethi)

Phaneritic rocks, like this diorite, have mineral grains large enough to

be seen with the naked eye.

Rapid cooling occurs near or on the earths surface, and

produces aphaniticor glassy texture. Aphanitic means that mineral

grains are too small to be seen with the naked eye.

(Leftphotograph by Phyllis Newbill, right photograph by Parvinder Sethi)

Aphanitic rocks, like this andesite (left) and basalt (right) have mineral

grains too small to be seen with the naked eye.


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Texture (Part 2)

Other textural terms are used to describe igneous rocks.

Porphyriticrocks contain mineral crystals of various sizes. Some

grains are distinctly larger than others.

Porphyritic Texture (Photograph by Stan Johnson)

Porphyritic rocks, like this one, have mineral grains of very different

sizes.

Vesiculartexture refers to volcanic rocks that contain holes calledvesicles that were formed by gas bubbles in lava.


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Scoriawith vesicular texture (Photograph by Parvinder Sethi)

This igneous rock is called scoria. It has vesicular texture. Thevesicles form from escaping gas bubbles in cooling lava.

Pyroclasticrocks are composed of broken fragments and formed by

volcanic eruptions.


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Tuff, Mount Rogers Formation (Photograph by

Parvinder Sethi)

Rocks with pyroclastic textureare made of broken

fragments. This rock, called tuff,consists of fine fragments

created during a volcaniceruption. Larger fragments arepresent in this sample from the

Mount Rogers area of Grayson

County.

Pegmatitictexture refers to intrusive igneous rocks called

pegmatites with unusually large mineral grains. Some individualgrains can be several feet long.


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(Photograph by Parvinder Sethi)

Pegmatites have very large

crystals. This photograph showsa part of an Amelia County

pegmatite on display at theNational Museum of Natural

History in Washington

D.C. Crystals in the pegmatitecan be several feet long.

Composition (Part 1)

Igneous rocks are also classified based on the minerals that make

them up. Igneous minerals occur in groups called mineral

assemblages.

Mafic Minerals

Dark-colored minerals such as olivine, pyroxene, amphibole, biotite,

and calcium-rich plagioclase feldspar tend to occur together. Theyform dark-colored igneous rocks described as mafic.


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Typical minerals found in mafic rocks (Photographs by Parvinder Sethi)

Mafic minerals include olivine (top left), pyroxene (top right),

amphibole (bottom left), and biotite (bottom right). These mineralsare dark-colored and often occur together in mafic igneous rocks.



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Gabbro, shown here, is an example of a mafic igneous rock. Note the

dark, bluish-gray crystals of calcium-rich plagioclase feldspar.

Felsic Minerals

Light-colored minerals such as muscovite mica, orthoclase feldspar,

sodium-rich feldspar, and quartz tend to occur together. They formlight-colored igneous rocks described as felsic.

Typical minerals found in felsic rocks (Photographs by Parvindter Sethi)

Felsic minerals include muscovite (top left), sodium-rich plagioclase

feldspar (top right), orthoclase feldspar (bottom left), and quartz

(bottom right). These minerals are light-colored and often occurtogether in felsic igneous rocks.


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Granite(Photograph by Parvinder Sethi)

Granite, shown here, is an example of a felsic igneous rock. Lightcolored grains are quartz and orthoclase feldspar. Small black crystals

are biotite mica.

Common Igneous Rocks (Part 1)

1.Granite

2.Gabbro

3.Diorite

4.Peridotite

5.Rhyolite

6.Basalt

7.Andesite

8.Obsidian

9.Scoria
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10.Pumice

11.Tuff

12.Volcanic Breccia

GraniteGranite is a phaneritic, felsic igneous rock composed primarily of

quartz and feldspar. Granite occurs in a variety of colors, but isusually white, light gray, or pink.

Granite (Photograph by Parvinder Sethi)

Gabbro

Gabbro is a phaneritic, mafic igneous rock composed primarily ofcalcium-rich feldspar, pyroxene, and olivine.
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Gabbro (Photograph by Parvinder Sethi)

Diorite

Diorite is a medium-colored (or intermediate), phaneritic igneous

rock. This sample is composed of light-colored orthoclase feldsparand quartz crystals and dark-colored hornblende.


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Diorite (Photograph by Parvinder Sethi)

Peridotite

Peridotite is a phaneritic, mafic igneous rock. This sample is

composed entirely of olivine.


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Peridotite (Photograph by Parvinder Sethi)

Rhyolite

Rhyolite is an aphanitic, felsic igneous rock composed primarily of

orthoclase feldspar and quartz. A few larger crystals of orthoclasefeldspar are visible in this sample.


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Rhyolite (Photograph by Parvinder Sethi)

Basalt

Basalt is an aphanitic, mafic igneous rock. Its dark color is due to its

dark-colored mineral composition.


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Basalt (Photograph by Parvinder Sethi)

Andesite

Andesite is an aphanitic, intermediate igneous rock. Larger, dark-

colored crystals in this example of andesite are hornblende.


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Andesite (Photograph by Parvinder Sethi)

Obsidian

Obsidian is a glassy igneous rock. Extremely rapid cooling of volcanicmaterial prevents crystal development and creates this volcanic glass.


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Obsidian (Photograph by Parvinder Sethi)

Scoria

Scoria is an igneous rock with vesicular texture. The vesicles, or holes,

in the rock form from bubbles of volcanic gas. Scoria forms the crustof lava flows.


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Scoria (Photograph by Parvinder Sethi)

Pumice

Pumice is another volcanic igneous rock with vesicular texture. Pumiceis less dense and lighter colored than scoria. It is commonly identified

by its scratchy surface and low density.


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Pumice (Photograph by Phyllis Newbill)

Tuff

Tuff is an igneous rock with pyroclastic texture. Tuffs consist of fine-

grained fragments created during volcanic eruptions. Some largerfragments are visible in this specimen.


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Tuff (Photograph by Parvinder Sethi)

Volcanic Breccia

Volcanic breccia is an igneous rock with large, angular fragments of

volcanic material. This breccia probably formed during a violentvolcanic eruption.


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Volcanicbreccia (Photograph by Parvinder Sethi)

Sedimentary Rocks

Sedimentary rocks form from the accumulation of sediment at earthssurface. Most sedimentary rocks are layered. Sedimentary rocks can

form from grains of pre-existing rocks (detritus), from chemical

processes, or from organic processes. They are classified based ontheir texture and composition.

Topics:

1.Origins of sedimentary rocks

2.Classification

3.Common sedimentary rocks

4.Special sedimentary rocks

Origins of Sedimentary Rocks (Part 1)

Sedimentary rocks can form from grains of pre-existing rocks

(detritus), from chemical processes, or from organic processes.
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Detrital Sedimentary Rocks

Detritalsedimentary rocks form from detritus, the rock and mineral

fragments that are transported by gravity, water, ice, or wind. Detritalsediments are classified by grain size.

Detritus is classified by its grain size. Grains larger than 2 millimetersare calledgravel. Grains between 1/16 mm and 2 mm are

calledsand. Grains smaller than 1/16 mm are in thesiltandclaysizeranges, often referred to as mud.

Detrital

sediments (Photograph by Parvinder Sethi)


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Albemarle County conglomerate (Photographby Parvinder Sethi)

This Albemarle Countyconglomerate is an example of adetrital sedimentary rock. It

contains gravel and sand

grains. Note dime for scale.

Chemical Sedimentary

Rocks

Chemicalsedimentary rocks form from sediment particles that were

inorganically precipitated from liquids. Examples include limestone

and gypsum.


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Microcrystalline limestone (Photograph by Parvinder Sethi)

Microcrystalline limestone is an example of an inorganically

precipitated sedimentary rock. This rock formed when water wassaturated with calcium carbonate that precipitated as tiny crystals of

calcite.

Organic Sedimentary Rocks

Organicsedimentary rocks form from the action oforganisms. Examples include fossiliferous limestone and coal.

Left:

Fossiliferous limestone (Photograph by Stan Johnson); right: Coal (Photograph by Phyllis Newbill)


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Fossiliferous limestone and coal

are two examples of organically-formed sedimentary rocks. This

fossiliferous limestone (left) isfrom Giles County, and was

formed from the shells of many

aquatic organisms. This coal(right) is from Wise County, andis the remains of ancient plants.

Classification of Sedimentary Rocks (Part 1)

Sedimentary rocks are classified based on their texture and

composition. Detrital sediment has a clastic(broken)texture. Chemical and organic sediments have a non-clastictexture,

and are classified based solely on their composition.

Clastic Texture

Clastic rocks are named for their grain size and shape.

Coarse-grained(>2 mm) rocks with rounded grains are

calledconglomerate. If the coarse-grains are angular, the rocks are

calledbreccia.

Left: conglomerate; right: sedimentary breccia (Photographs by Stan Johnson)

Conglomerates (left) are

coarse-grained sedimentary

rocks with roundedgrains. This sample is fromLoudoun County. Breccias(right) are coarse-grained

sedimentary rocks with angular


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grains. This sample is from Culpeper County. Note quarters for scale.

Medium-grained(1/16 mm to 2 mm) rocks are usuallycalledsandstone. Medium-grained rocks can be composed of quartz

grains, feldspar grains (arkose), or rock fragments and clay(graywacke).

Sandstone (Photograph by Parvinder Sethi)

Medium-sized grains in clastic sedimentary rocks form sandstone. This

sample is a quartz sandstone.

Fine-grained(


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Shalefrom Grayson County (Photograph by

Parvinder Sethi)

Fine-grained sediments usuallyform shale. Shale is a detrital

sedimentary rock that splits

readily along thin beddingplanes. This sample is from

Grayson County in the Mount

Rogers area.

Non-clastic Texture

Non-clastic rocks have chemical or organic origins. Names of non-

clastic rocks are based on their compositions.

A calcite-rich rock with many fossils is called a fossiliferous

limestone.

Microcrystalline quartz is called chert. The red variety of chert iscalled jasper. Dark gray to black chert is called flint.

The carbon-rich rock formed from ancient plant material is calledcoal.


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Left: fossiliferous limestone; right: chert (Photographs by Parvinder Sethi)

Coal (Photograph by Parvinder Sethi)

Sedimentary rocks with non-clastic texture include fossiliferous

limestone (above left), chert (above right) and coal (right). All threeof these rock types can be found in Virginia.

Composition of Sedimentary Rocks (Part 1)

Sedimentary rocks are also classified based on their mineralcomposition. Common minerals in sedimentary rocks include:

Quartz

Calcite

Clay minerals

Dolomite

Gypsum and halite

Feldspar and mica

Quartz
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Quartz is an extremely stable mineral, both mechanically and

chemically. It is a major component of sandstone and chert. Thisphotograph shows a sample of chert.

Chert(Photograph by Parvinder Sethi)

Calcite

Calcite forms limestone through chemical and biologicalprocesses. Limestone is a very common sedimentary rock. The small

gray mineral grains and the white fossil grains in this rock are both

composed of calcite.


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Fossiliferous limestone (Photograph by Parvinder Sethi)

Clay Minerals

Clay minerals usually form fine-grained rocks like this shale. Clayminerals are a group of flaky silicate minerals that form from the

weathering of pre-existing rocks and minerals. Clay is the single most

abundant type of sediment.


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Shale (Photograph by Parvinder Sethi)

Dolomite

Dolomite forms the rock dolostone. It forms when some of the calcium

in calcite is replaced by magnesium. The large white crystals on thissample are dolomite. The entire rock is dolostone.

Gypsum and Halite

Gypsum, shown left, and halite, shown right, are common examples

ofevaporiticsedimentary rocks. Both gypsum and halite form inextremely warm, arid environments.


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Left: gypsum; right: halite (Photographs by Parvinder Sethi)

Feldspar and Mica

Feldspar and mica are common silicate minerals that are found in

detrital sedimentary rocks.

Left: feldspar; right: mica (Photographs by Parvinder Sethi)

Common Sedimentary Rocks (Part 1)

Conglomerate

Sandstone

Shale

Limestone

Dolostone

Chert

Conglomerate
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Conglomerate is a detrital sedimentary rock with rounded, gravel-sized

grains.

Conglomerate (Photograph by Stan Johnson)

This Albemarle County

conglomerate is a good

example. It contains gravel andsand grains. Note dime for

scale.

Sandstone

Sandstone, shown with sand, is a detrital sedimentary rock with clastic

texture. Sandstone can be identified by its sandy feel and grainsize. This sample is a quartz sandstone. Note quarter for scale.


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Sandstone (Photograph by Parvinder Sethi)

Shale

Shale is a detrital sedimentary rock with clastic texture. It can beidentified by its fine grains and the way it splits apart along thin

layers.


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Shale(Photograph by Parvinder Sethi)

This sample is from Grayson

County in the Mount Rogersarea.

Limestone

Limestone is a very commonsedimentary rock. It is often

made up of various sizes of

animal shells. Limestone fizzes

with the application of dilute hydrochloric acid because it containscalcite.


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Limestone (Photograph by Parvinder Sethi)

Dolostone

Dolostone is a common sedimentary rock similar to limestone. It is

typically a dull gray. It can be identified by scratching the surface andexposing the scratches to dilute hydrochloric acid. Only the scratches

on dolostone will fizz.


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Dolostone (Photograph by Parvinder Sethi)

Chert

Chert is a chemical sedimentary rock composed of microcrystalline

quartz. In its gray form, it is called flint. It makes sparks when struckagainst steel.


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Chert(Photograph by Parvinder Sethi)

Special Sedimentary Rocks

There are many types of sedimentary rocks. The sedimentary rockslisted here are interesting or have economic importance.

Travertine is a calcite-rich rock found in cave formations. Tufa is aporous rock formed near calcareous springs.


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Stalactites (Photograph by Parvinder Sethi)

Travertine is the rock that makes up most cave deposits, including the

stalactites in this picture. Deposits that form this way are alsocalleddripstone.

Chalkis a kind of limestone made of a mixture of calcite-rich andsilica-rich organic remains.

Coquina is a kind of limestone made of weakly cemented, brokenanimal shells. Coquinas form in beach and shallow water environments

where waves break apart animal shells.


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Coquina (Photograph by Parvinder Sethi)

Coalis a biochemical sedimentary rock made up of compacted

ancient vegetation formed in swamps.

Coal (Photograph by Parvinder Sethi)


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Dolomite (Photograph by Parvinder Sethi)

Metamorphic Rocks

Metamorphic comes from the Latin words for changed form, and refers

to rocks that formed by changing pre-existing rocks with heat,pressure, or chemical activity that occurs under conditions of heat and

pressure. Metamorphic rocks are classified based on their texture and

composition.

Topics:

1.Agents of metamorphic change

2.Classification:Foliated Textures,Non-foliated textures,andComposition

3.Common metamorphic rocks

AGENTS OF METAMORPHIC CHANGE
http://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5.html#Agentshttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5.html#Agentshttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5.html#Agentshttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5a.htmlhttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5a.htmlhttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5a.html#Foliatedhttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5a.html#Foliatedhttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5a.html#Foliatedhttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5c.htmlhttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5c.htmlhttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5d.htmlhttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5d.htmlhttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5f.htmlhttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5f.htmlhttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5f.htmlhttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5d.htmlhttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5c.htmlhttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5a.html#Foliatedhttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5a.htmlhttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5.html#Agents


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The range of temperatures at which metamorphic activity takes place

is between 300 and 1470 degrees Fahrenheit. Heat sources includemagma, geothermal heat, and friction along faults.

Pressure sources include the weight of overlying rocks deep in theearth. Shear pressure in fault zones can metamorphose rocks at

shallower depths.

Chemical activity is usually caused by water at higher temperatures

and pressures. Water acts to dissolve pre-existing rocks, to transportdissolved materials, and to catalyze chemical changes.

Classification of Metamorphic Rocks (Part 1)

Metamorphic rocks are classified based on their texture and

composition. Metamorphic textures can be foliated or non-foliated.

1.Foliated texture

2.Non-foliated texture

3.Composition

Foliated Textures

Afoliatedtexture is caused by pressure. Mineral grains from pre-

existing rocks are oriented parallel to each other or organized intodistinctive bands during metamorphosis. Examples of foliated textures

includeslaty,phyllitic,schistose, andgneissic.

Slaty Texture

Rocks with a slaty texture are fine-grained. They have dull surfaces

and split apart easily.
http://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5a.html#Foliatedhttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5a.html#Foliatedhttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5c.htmlhttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5c.htmlhttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5d.htmlhttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5d.htmlhttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5a.html#Slatyhttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5a.html#Slatyhttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5a.html#Slatyhttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5a.html#Phyllitichttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5a.html#Phyllitichttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5b.html#Schistosehttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5b.html#Schistosehttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5b.html#Gneissichttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5b.html#Gneissichttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5b.html#Gneissichttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5b.html#Schistosehttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5a.html#Phyllitichttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5a.html#Slatyhttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5d.htmlhttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5c.htmlhttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5a.html#Foliated


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Redslate (Photograph by Parvinder Sethi)

Rocks with slaty texture, like this red slate, split apart easily. Grains inslaty rocks are too small to see with the naked eye.

Phyllitic Texture

Phyllitic rocks have very small grains and shiny, crenulated (crinkled)surfaces. They also split apart easily.


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Phyllite(Photograph by Parvinder Sethi)

Rocks with phyllitic texture, like this green phyllite, are slightly more

metamorphosed than those with slaty texture. This sample has weakcrenulation bands on its surface.

Foliated Textures (Continued)

Schistose Texture

Schistose rocks have visible grains. They are most commonly made

up of platy minerals like mica.


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Schist(Photograph by Parvinder Sethi)

Rocks with schistose texture, like this garnet schist, are more

metamorphosed than those with phyllitic texture. Schists can formfrom a variety of parent rocks.

Gneissic Texture

Gneissic rocks have minerals separated into light and dark bands.


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Gneiss(Photograph by Parvinder Sethi)

Non-Foliatied Texture

Non-foliated metamorphic rocks appear massive or granular without

the characteristic parallel mineral grains in foliated rocks.

Non-foliated metamorphic rocks are classified based primarily ontheir composition.

Marble, quartzite, and soapstone are examples of non-foliated

metamorphic rocks.

Left:marble (photograph by Stan Johnson); right: quartzite (photograph by Parvinder Sethi)


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Marble (left) and quartzite (right)

are non-foliated metamorphicrocks. This marble sample is

from AlbemarleCounty. Quartzite is mined in

Wythe County.

Composition

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 thegrade of metamorphism.

Index Minerals minerals include chlorite, epidote, garnet, staurolite,

kyanite and sillimanite.

Fine-grained crystals ofchlorite (not visible) give this slate its green

color. Chlorite is a complex silicate mineral formed during low-grade

metamorphism.


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Slate(Photograph by Parvinder Sethi)

Green crystals ofepidote are visible in this sample ofunakite. Epidote is a complex silicate mineral formed during low- to

medium-grade metamorphism.


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Unakite(Photograph by Parvinder Sethi)

Classification of Metamorphic Rocks (Part 5)

Dark and red-brown crystals ofgarnetin schist indicate medium-grade metamorphism. Garnet is an aluminum-rich silicate mineral.


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Schist(Photograph by Parvinder Sethi)

Elongated brown crystals ofstaurolite in schist indicate medium- to

high-grade metamorphism. Staurolite is commonly known as fairystone. Staurolite contains iron, magnesium, aluminum, and silicate.


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Staurolite (Photograph by Parvinder Sethi)

Bladed blue crystals ofkyanite in schist indicate high-grade

metamorphism. Kyanite is made up of aluminum and silicate.


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Kyanite(Photograph by Parvinder Sethi)

Common Metamorphic Rocks, Part 1

Slate

Phyllite

Schist

Gneiss

Amphibolite

Marble

Quartzite

Soapstone

Slate

Slate is a fine-grained, low-grade metamorphic rock. It forms from themetamorphism of the sedimentary rock shale.
http://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5f.html#Slatehttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5f.html#Slatehttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5f.html#Slatehttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5f.html#Schisthttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5f.html#Schisthttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5f.html#Schisthttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5g.html#Schisthttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5g.html#Schisthttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5g.html#Schisthttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5g.html#Gneisshttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5g.html#Gneisshttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5g.html#Gneisshttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5g.html#Amphibolitehttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5g.html#Amphibolitehttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5g.html#Amphibolitehttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5h.html#Marblehttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5h.html#Marblehttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5h.html#Marblehttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5h.html#Quartzitehttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5h.html#Quartzitehttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5h.html#Quartzitehttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5h.html#Soapstonehttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5h.html#Soapstonehttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5h.html#Soapstonehttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5h.html#Soapstonehttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5h.html#Quartzitehttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5h.html#Marblehttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5g.html#Amphibolitehttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5g.html#Gneisshttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5g.html#Schisthttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5f.html#Schisthttp://www.radford.edu/jtso/GeologyofVirginia/Rocks/GeologyOfVARocks2-5f.html#Slate


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Slate(Photograph by Parvinder Sethi)

Phyllite

Phyllite is a fine-grained, low-grade metamorphic rock. It is slightlymore metamorphosed than slate, and tends to have a crenulated or

crinkled surface.


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Phyllite(Photograph by Parvinder Sethi)

1.2 Mineral Identification

1.3 Major Mineral Groups

1.4 Selected Virginia Minerals

1.5 Tips for Mineral Collecting

Schist

Schist is a medium- to high-grade metamorphic rock. It is usuallyshiny and crinkled.


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Kyanite Schist (Photograph by Stan Johnson)

This sample is from Buckingham

County.

Gneiss

Gneiss is a high-grade metamorphic rock characterized by alternating

bands of dark and light minerals.


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Gneisses (Photographs by Stan Johnson)

These samples are fromHanover County (left) and

Buckingham County (right).

Amphibolite

Amphibolite is a hornblende-rich foliated metamorphic rock thatindicates medium- to high-grade metamorphism.


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Amphibolite (Photograph by Bill Henika)

This amphibolite is from Halifax

County.

Marble

Marble is a non-foliatedmetamorphic rock formed from the metamorphism of limestone ordolomite.


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(Photographs by Stan Johnson)

These marble samples are fromAppomattox County (left) and

Albemarle County (right).

Quartzite

Quartzite is a non-foliated metamorphic rock formed from themetamorphism of quartz sandstone.


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Soapstone

Soapstone is a non-foliated metamorphic rock composed of

talc. Soapstone is a favorite of sculptors because of its softness.


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Soapstone (Photograph by Parvinder Sethi)

Types of Rocks

Igneous Rocks- form when hot, liquid rock (magma) cools and solidifiesExtrusive igneous rock- forms from magma that erupts onto the

earths surface. It is common around volcanoes. It cools quickly on the surface and contains very small or no

crystals.

Intrusive igneous rock- forms when magma cools below the earths

surface. The magma cools slowly and forms large, visible crystals.

Sedimentary Rocks- form at or near the Earths surface. It forms without the

heat and pressure that are involved in the formation of igneous or metamorphic rocks. Formed of weathered

rock/mineral fragments, crystallized minerals, or from the remains of once-living plants and animals.

Metamorphic Rocks- Forms when rocks are exposed to intense heat,

pressure, or a combination of both.

Contact metamorphism- When a rock changes to ametamorphic rock through heating from nearby magma

Regional metamorphism- When a rock changes to a

metamorphic rock due to the pressure from the Earth above it.


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A Diagram of the Rock Cycle

You have a few other science-related items to keep in mind this week:

1. Your three choices from your Hard Rock Cafe menu are due Friday.

2. A science journal entry will be due Thursday. Please write at least five thoughtful sentences in response to the

prompt.

3. As you finish your menu sheet, I will have three choice labs associated with the rock cycle that you are more than

welcome to explore. Please remember that only two people at a time can work on each lab, copy the lab procedures

and answer questions on a piece of notebook paper to be submitted to me, and return the lab materials to their

original condition once the lab is completed.

4. Ms. Diane has a really fun and tasty activity she would like to share with you where you will make edible

representations of sedimentary, igneous, and metamorphic rocks!

Finally, since Friday is the last Friday of the month, it is a dress down day! But, I want everyone to wear a smile that

day, too because it is also Fall picture day! Mr. Charles just gave word that picture day will be rescheduled. BUT,

Friday is still a dress down day!

See you Monday morning,

Mr. Trent
http://3.bp.blogspot.com/-ONqZV6VD7Bs/UF3DwFjgbtI/AAAAAAAAEKM/D9dE_AKE9_Y/s1600/rock+cycle.png

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