Igneous rocks are formed by solidification of molten rock material. There are two types of igneous rocks, Intrusive (plutonic) - form below the Earth’s surface, and extrusive is volcanic which forms above the earths surface. These intrusive igneous rocks cool slowly deep within the earth and produces large crystals. Intrusive igneous rocks will result in a very coarse (pegmatite) or coarse (phaneritic) texture (ex. granite). Intrusive rocks and some examples of Intrusive igneous rocks are diorite, gabbro, granite, and pegmatite. The other is extrusive rocks and examples of extrusive rocks are andesite, basalt, obsidian, pumice, rhylite, and scoria. The difference between extrusive opposed to intrusive rocks. Extrusive rocks are formed above the Earth’s surface. Lava is molten rock that pours out onto the Earth’s surface. Extrusive igneous rocks will result in fine texture. If the cooling is instantaneous a glassy texture may form. If gas bubbles are trapped as the lava quickly cools a vesicular texture, pumice, may occur. Some types of Igneous rocks are, Granite- quartz, orthoclase feldspar, and at least one other mineral; light-colored; coarse-grained; makes up continents; felsic. Ryolite- fine-grained granite; felsic. Obsidian- volcanic glass; rapid cooling; pyroclastic; felsic. Pumice- sponge-like because of escaping air bubbles during cooling; felsic. Basalt- fine-grained; dark-colored; makes up the ocean floor; mafic. Gabbro- coarse-grained basalt; mafic. Diabase- grain size inbetween basalt and gabbro; mafic. Basalt glass- mafic obsidian. Scoria- mafic pumice
What is an Igneous Rock

  • An igneous rock is one of the three rock types.
  • An igneous rocks are that form when molten rock cools or crystallizes.
  • Igneous rocks make up approximately 90% of the upper part of Earth's crust.
Classifying Igneous Rocks

  • Igneous rocks are based on mineral, crystal size, and texture.
  • Texture is used to subdivide igneous rocks into four groups Glassy, Fined grained, course, and very course grained.
Mineral Composition

  • Rock type can be determined by estimating the relative percentages of mineral in the rocks.
Intrusive Igneous Rocks

  • An Intrusive Igneous rock is when magma is underground and it cools and hardens. Rocks that form in this are called Intrusive Igneous Rocks.
  • There are many types of Igneous rocks but the rock Granite is the most common intrusive igneous rock.
Extrusive Igneous Rocks
  • An Extrusive Igneous Rock forms when molten rock reaches the Earth's surface.
Vesicular Rocks

  • Vesicular is a type of texture when there is a spongy appearance in the Rock
  • Vesicular has holes
  • An example of a vesicular rock is Pumice.
Texture

  • Porphyritic has large well formed crystals surrounded by finer grain crystals.
Here are Igneous Rocks.
andesite.jpg
andesite.jpg

Andesite is a fine-grained, extrusive igneous rock composed mainly of plagioclase with other minerals such as hornblende, pyroxene and biotite.
basalt.jpg
basalt.jpg

Basalt: a fine-grained igneous rock that is usually black in color. The specimen shown is about two inches (five centimeters) across.
quartz-diorite.jpg
quartz-diorite.jpg

Diorite is a coarse-grained, intrusive igneous rock that contains a mixture of feldspar, pyroxene, hornblende and sometimes quartz
gabbro.jpg
gabbro.jpg

Gabbro is a coarse-grained, dark colored, intrusive igneous rock that contains feldspar, augite and sometimes olivine.
granite-coarse-grained.jpg
granite-coarse-grained.jpg

Granite is a coarse-grained, light colored, intrusive igneous rock that contains mainly quartz and feldspar minerals.
obsidian.jpg
obsidian.jpg

Obsidian is a dark-colored volcanic glass that forms from the very rapid cooling of molten rock material. It cools so rapidly that crystals do not form.
pegmatite.jpg
pegmatite.jpg

Pegmatite is a light-colored, extremely coarse-grained intrusive igneous rock. It forms near the margins of a magma chamber during the final phases of magma chamber crystallization. It often contains rare minerals that are not found in other parts of the magma chamber.

peridotite.jpg
peridotite.jpg

Peridotite is a coarse-grained intrusive igneous rock that is composed almost entirely of olivine. It may contain small amounts of amphibole, feldspar, quartz or pyroxene.

pumice.jpg
pumice.jpg

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.

rhyolite.jpg
rhyolite.jpg

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

scoria.jpg
scoria.jpg
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.

welded-tuff.jpg
welded-tuff.jpg

Welded Tuff is a rock that is composed of materials that were ejected from a volcano, fell to Earth, and then lithified into a rock. It is usually composed mainly of volcanic ash and sometimes contains larger size particles such as cinders.






Sedimentary Rocks

S
edimentary rocks are formed from particles of sand, shells, pebbles, and other fragments of material. Together, all these particles are called sediment. Gradually, the sediment accumulates in layers and over a long period of time hardens into rock. Generally, sedimentary rock is fairly soft and may break apart or crumble easily. You can often see sand, pebbles, or stones in the rock, and it is usually the only type that contains fossils. There are 3 kinds of sedimentary rocks. Clastic Sedimentary rocks, Chemical also known as Crystalline Sedimentary Rocks, and Organic Rocks. Clastic sedimentary rocks are formed from solid fragments of other rocks, sandstone, shale, and conglomerate are all examples of clastic rocks. Sandstone is mostly composed of quartz grains, permeable, is an example of this. Shale is formed from the tiny flakes of clay which is compacted, impermeable, is the proof for this. Conglomerate could be classified as large round pebbles, which are cemented together. Breccia is known to have angular fragments which is the opposite of a conglomerate rock. Dolostone, rock salt, and rock gypsum are proven to be chemical sedimentary rocks. The main cause for these rocks to be dissolved is because of the amount of precipitation and evaporation they go through. This usually occurs in a shallow sea environment. An organic sedimentary rock is formed from the remains of plants and animals, some examples of this would be, coal; which is decayed plants and swamps is an important one. Also limestone rock, but it comes in handy when you want to do a HCL test. and hydrocloricacid test shows if a rock is limestone. you know it is when the rock fizzes with bubbles.


The Rock Cycle

The rock cycle is an illustration that is used to explain how the three rock types are related to each other and how Earth processes change a rock from one type to another through geologic time. Plate tectonic movement is responsible for the recycling of rock materials and is the driving force of the rock cycle





Metamorphic Rocks:

A metamorphic rock is the undergone transformation by heat, pressure, or other natural agencies, in the folding of strata or the nearby intrusion of igneous rocks.


Heat

-Heat sources for metamorphism are
Geothermal gradient, and Contact Metamorphism. Geothermal Gradient is when temperature increases with depth at a rate of 20 - 30 degrees C per km in the crust. Metamorphic mans to change from one form to another.

Pressure

The rocks are under tons and tons of pressure, which fosters heat build up, and this causes them to change.
-Burial Pressure
. Pressure increases with depth due to the weight of the overlying rocks. A cubic foot of granite weighs 167.9 pounds. Increase of pressure and temperature with depth causes Regional Metamorphism. Regional metamorphism occurs at depths of 5 - 40 km. Tectonic pressures associated with convergent plate boundaries and continental collision also cause Regional Metamorphism. Pressure along fault zones causes Dynamic Metamorphism, the crushing and ductile flow of rock. Rocks formed along fault zones are called mylonites.

Natural Agencies

In some metamorphic settings, new materials are introduced by the action of
hydrothermal solutions (hot water with dissolved ions). Many metallic ore deposits form in this way.

  • Metamorphic rocks are rocks that have changed from one form to another.
  • These rocks form deep in the earth where the it is very hot and there is a lot of pressure.
  • If a rock is heated and squeezed for millions of years, it can turn into a new kind of rock.
  • Metamorphic rocks begin to form at 12-16 kilometers (7.5 - 10 miles) beneath the surface of the earth.
  • They begin changing at temperatures of 100 - 800 degrees Celsius (212 - 1472 degrees Fahrenheit)
  • The heat in the earth comes from Magma and the pressure comes from layers of rock piled onto layers of rock.
  • The layers on the bottom get squeezed and the thicker the layers the more pressure or the more they get squeezed.



amphibolite-2.jpg
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. The specimen shown above is about two inches (five centimeters) across.
gneiss.jpg
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. The specimen shown above is about two inches (five centimeters) across.

hornfels.jpg
Hornfels is a fine-grained nonfoliated metamorphic rock with no specific composition. It is produced by contact metamorphism. Hornfels is a rock that was "baked" while near a heat source such as a magma chamber, sill or dike. The specimen shown above is about two inches (five centimeters) across.


marble.jpg Marble is a non-foliated metamorphic rock that is produced from the metamorphism of limestone. It is composed primarily of calcium carbonate. The specimen shown above is about two inches (five centimeters) across.

phyllite.jpg
Phyllite is a foliate metamorphic rock that is made up mainly of very fine-grained mica. The surface of phyllite is typically lustrous and sometimes wrinkled. It is intermediate in grade between slate and schist. The specimen shown above is about two inches (five centimeters across).

quartzite.jpg
Quartzite is a non-foliated metamorphic rock that is produced by the metamorphism of sandstone. It is composed primarily of quartz. The specimen above is about two inches (five centimeters) across.

chlorite-schist.jpg
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. The specimen shown above is a "chlorite schist" because it contains a significant amount of chlorite. It is about two inches (five centimeters) across.

garnet-schist.jpg 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. The specimen shown above is a "garnet schist" because it contains a significant amount of garnet. The small crystals visible in the rock are small red garnets. It is about two inches (five centimeters) across.

muscovite-schist.jpg

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. The specimen shown above is a "muscovite schist" because it contains a significant amount of muscovite mica. It is about two inches (five centimeters) across.


slate.jpg

Slate is a foliated metamorphic rock that is formed through the metamorphism of shale. It is a low grade metamorphic rock that splits into thin pieces. The specimen shown above is about two inches (five centimeters) across.



*I movie Script*

Brianna: Igneous, Sedimentary, Metamorphic Rocks: by: Brianna Marji, Erin O’connor, Alban Hoxhaj

Erin: Brianna, can you tell me what an igneous rock is?

Brianna: igneous rocks are intrusive or extrusive rocks formed from the cooling and crystallization of magma or lava.

Erin: Alright, so what is and intrusive rock?

Brianna: Intrusive (plutonic) - form below the Earth’s surface, and extrusive is volcanic which forms above the earths surface. These intrusive igneous rocks cool slowly deep within the earth and produces large crystals. Intrusive igneous rocks will result in a very coarse (pegmatite) or coarse (phaneritic) texture (ex. granite)

Erin: So is there a difference between extrusive opposed to intrusive?

Brianna: Yes, these two types of igneous rocks are almost the opposite from each other. Extrusive rocks are formed above the Earth’s surface. Lava is molten rock that pours out onto the Earth’s surface. Extrusive igneous rocks will result in fine texture. If the cooling is instantaneous a glassy texture may form. If gas bubbles are trapped as the lava quickly cools a vesicular texture, pumice, may occur.

Erin: Alright, so the difference between intrusive and extrusive result in a different manor, what are some common igneous rocks?

Brianna: Granite- quartz, orthoclase feldspar, and at least one other mineral; light-colored; coarse-grained; makes up continents; felsic. Ryolite- fine-grained granite; felsic. Obsidian- volcanic glass; rapid cooling; pyroclastic; felsic. Pumice- sponge-like because of escaping air bubbles during cooling; felsic. Basalt- fine-grained; dark-colored; makes up the ocean floor; mafic. Gabbro- coarse-grained basalt; mafic. Diabase- grain size inbetween basalt and gabbro; mafic. Basalt glass- mafic obsidian. Scoria- mafic pumice

Erin: Okay thanks Brianna, this gave me a better understanding of igneous rocks. OMG I heard mr. felipe talking to mr. chiara, about he is going to give us a pop quiz on sedimentary rocks, is there anything you would like to go over to get ready for this quiz?

Brianna: Yes! That would be great, I would really like to pass this quiz, it could sure bring up my grade. Can you explain sedimentary rocks to me?

Erin: Me too, I sure do need a good grade. A sedimentary rock is a rock that forms from the total sediments that come from preexisting rocks and/ or organic materials.

Brianna: how many types of sedimentary rocks are there?

Erin: There are 3 kinds of sedimentary rocks. Clastic Sedimentary rocks, Chemical also known as Crystalline Sedimentary Rocks, and Organic Rocks.

Brianna: Can you explain more about these 3 kind of rocks ?

Erin: Sure, Clastic sedimentary rocks are formed from solid fragments of other rocks, sandstone, shale, and conglomerate are all examples of clastic rocks.

Brianna: well what is sandastone, shale, and conglomerate?

Erin: Sandstone is mostly composed of quartz grains, permeable, is an example of this. Shale is formed from the tiny flakes of clay which is compacted, impermeable, is the proof for this. Conglomerate could be classified as large round pebbles, which are cemented together. Breccia is known to have angular fragments which is the opposite of a conglomerate rock.

Brianna: Well im still a little rusty on the Chemical and Organic type of sedimentary rocks.

Erin: Alright, no problem gurl! Dolostone, rock salt, and rock gypsum are proven to be chemical sedimentary rocks. The main cause for these rocks to be dissolved is because of the amount of precipitation and evaporation they go through. This usually occurs in a shallow sea environment.

Brianna: Well I understand that an organic sedimentary rock is formed from the remains of plants and animals, but can you give me a few examples?

Erin: Of course, coal, which is decayed plants and swamps is an important one. Also limestone rock, but it comes in handy when you want to do a HCL test

Brianna: Well why is this?

Erin: the reason I feel this is the most exciting part, interests me, because if it is limestone it fizzes up with bubbles

Brianna: Oh wow, that’s so cool

Erin: Yes it is! But i found out that metamorphic rock is going to be on the quiz also. So, Brianna, what is a metamorphic rock?

Brianna: A metamorphic rock is a rock formed from existing rocks, meaning sedimentary igneous, and metamorphic rocks. These metamorphic rocks are shown by the action of heat, pressure, and chemicals

Erin: Ok, I understand, but please explain heat, pressure, and chemicals




Brianna: When rocks have been metamorphosed this means they have been changed. When this happens pressure and temperature increase with depth, when pressure and temperature becomes high enough, rocks melt and form magma

Erin: well, what happens if the temperature isn’t high enough?

Brianna: Well, when high temperature and pressure combine and change the texture, mineral composition, or chemical composition of a rock without melting it, a metamorphic rock forms.

Erin: Alright, I get it now. So what your trying to say is when the temp. isn’t high enough it forms a metamorphic rock, right?

Brianna: That’s right!

Erin: Great! Now lets discuss the rock cycle.

Brianna: Lets, the rock cycle is a continuous changing and remaking of rocks.

Erin: Do you have a chart of the rock cycle, so that I can get a visual description?

Brianna: Yeah, but I have to find it first…

Erin: Yea, that picture really gave me a good visual, thanks.

Brianna: Well I have to go finish my studying, I will see you tomorrow in class, good luck.

Erin: Alright, see you later.


http://www.learner.org/interactives/rockcycle/types2.html