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Presentation on theme: "Rocks."— Presentation transcript:

1 Rocks

2 What is a Rock A rock is a naturally occurring solid mixture composed of minerals, smaller rock fragments, organic material, or glass. The individual particles in a rock are known as grains.

3 Types of Rocks Igneous Sedimentary Metamorphic
There three main types of rocks: Igneous Sedimentary Metamorphic

4 Rock Cycle

5 Igneous Rock Igneous rocks are the most abundant form of rock on Earth. Igneous rocks are formed from magma or lava. The type of magma will determine what type of igneous rock will form. There four main types of magma: Felsic Intermediate Mafic Ultramafic

6 Felsic Magma Felsic magma is thick and slow moving. It contains large amounts of silica (SO2) and smaller amounts of calcium, iron and magnesium. Igneous rocks formed from felsic magma typically harden into light colored silicate minerals such as quartz and orthoclase feldspar.

7 Mafic Magma Compared to felsic magma, mafic magma is much hotter, thinner and faster moving. Mafic magma contains large amounts of iron and magnesium and very small amounts of silica. Rocks formed from mafic magma are much darker in color due to large amounts of dark silicate minerals such as biotite, augite, and hornblend, olivine, and pyroxene.

8 Bowen’s Reaction Series

9 Igneous rock There are two main types of igneous rock: Intrusive

10 Intrusive Igneous Rock
Intrusive igneous rocks form below the Earth’s surface and cool slowly. Characteristics of Intrusive igneous rock include: Course texture Large grains Large crystals. Light-colored

11 Extrusive Igneous Rock
Extrusive igneous rock forms when lava cools and crystallizes on the Earth’s surface. Characteristics of extrusive igneous rock include: Fine texture Small grains Small crystals. Dark-colored

12 Families of Igneous Rock
Igneous rock is classified into three families: Granite Family Gabbro Family Diorite Family

13 Granite Family Rocks in the granite family form from slow-rising, “sticky”, felsic magma that cooled slowly underground. Granite can only be seen at the surface as a result of uplift or weathering and erosion.

14 Dull with some pearly and glassy
Granite Family Properties Granite Obsidian Pumice Color Salmon, gray, black Smoky brown Light gray Luster Dull with some pearly and glassy Glassy Dull Hardness 7 5 -5.5 5 -5.6 Streak No streak or white White Break Fracture Conchoidal Density 2.6 – 2.7 g/cm3 2.6 g/cm3 .64 g/cm3 Specific Gravity 2.69 5 .64 Crystal Structure Anhedral None Special Properties - Floats

15 Granite Family Granite Obsidian Pumice

16 Gabbro Family Igneous rock forms from mafic magma. These rocks are dark in color, fine grained and denser than rock in the granite family.

17 Gabbro Family Scoria Olivine Basalt Reddish Brown Greenish Black
Properties Scoria Olivine Basalt Color Reddish Brown Greenish Black Black, Dark gray Luster Glassy Dull Hardness 5 - 6 7 Streak Reddish brown White Black Break Fracture Conchoidal Density 2.6 g/cm3 3.32 g/cm3 3 g/cm3 Specific Gravity .8 – 2.1 3.2 – 3.4 Crystal Structure None Orthorhombic Special Properties -

18 Gabbro Family Scoria Olivine Basalt Biotite Gabbro Pyroxene Plagioclase Feldspar

19 Diorite Family Rocks in the diorite family have an intermediate composition that is neither felsic nor mafic, but has characteristics of both. Their colors tend to be medium gray and greens.

20 Diorite Family Diorite Andesite Black, White, Salt and Pepper
Properties Diorite Andesite Color Black, White, Salt and Pepper Gray with black crystals Luster Glassy Hardness Streak Bluish black White Break Cleavage Conchoidal Density 2.7 g/cm3 2.5 – 2.8 g/cm3 Specific Gravity 3.2 – 3.4 Crystal Structure None Orthorhombic Special Properties -

21 Ultramafic Rocks Ultramafic rocks consist of mainly mafic minerals that are dark in color, coarse grain and dense. Rocks in this family include: Peridotite Dunite Pyroxenite

22 Igneous Intrusion Igneous intrusion occurs when magma forces its way into fractures in the bedrock. The magma cools, leaving a layer of igneous rock which is different than the surrounding rock. Intrusion will only be revealed only after overlaying has been eroded away or has been uplifted.

23 Types of Intrusions Pluton: A large, thick igneous rock mass that forms when magma cools within the Earth’s interior. Batholiths: The largest of all plutons. Batholiths form the core of many of Earth’s mountain ranges Laccolith: A dome-shaped mass of intruded igneous rock.

24 Types of Intrusion cont.
Dikes: Sheets of igneous rock that cut across rock layers vertically or at steep angles. Sills: Sheets of igneous rock that lie parallel to the layers of rock it intrudes. Volcanic Necks: The remains of a central vent of an extinct volcano. These necks are only revealed after all the surrounding rock has been weathered and eroded away.

25 Intrusions


27 Devil’s Tower

28 Sedimentary Rock Sedimentary rocks form through the compaction and cementation of layers of sediment. The single most characterizing feature of sedimentary rock is known as “Stratification”. Stratification is a change in type of sediment laid down resulting in the formation of a new rock. Bedding planes are lines between each different layer of sediment.

29 Formation of Sedimentary Rock
The process of forming a sedimentary rock is known as “Lithification”. There are three main processes of lithification: Clastic Process Chemical Process Organic Process

30 Clastic Process Clastic sedimentary rocks are formed from fragments of other rocks. The process begins with the movement and relocation of rock fragments mainly by moving water. When the fragments settle, (deposition), dissolved minerals, such as silica, calcite, iron oxide, and clay, in the water fill the empty spaces of the loose particles and cement them together. This process is called “cementation”

31 Clastic Rocks Conglomerate Breccia Sandstone Shale

32 Chemical Rocks Chemical rocks form with minerals dissolved in water precipitate from solution. Precipitation can occur by evaporation or chemical action. Chemical action: While in solution, dissolved ions combine to form new minerals. Examples of chemical action are: Rock Salt, Halite, Gypsum, and Limestone

33 Organic Process Organic sedimentary rock forms from sediment containing the remains of plants and animals. Common organic sedimentary rocks are limestone and coal.

34 Organic Limestone Organically formed limestone contains the mineral calcite. The process begins when water dissolves calcite out of rocks on land and carries it in the form of ions to lakes or oceans. Certain aquatic organisms, such as clams, corals and some algae, use the ions to produce calcium carbonate shells. When these organisms die, their shells fall to the ocean floor and begin to pile up. Over time, other minerals in the ocean cement the shells together to form coquina.

35 Organic Limestone cont.
Coquina is broken down into fragments by ocean waves and these fragments are cemented together into limestone. Limestone formed near shore contain large amounts of clay. Limestone that forms farther from shore are almost pure calcite.

36 Formation of Coal

37 Formation of Coal Peat Lignite Bituminous Anthracite


39 Coal in Pennsylvania

40 Features of Sedimentary Rock
Fossils: Fossils are the remains, impressions, and any other evidence of plants or animals preserved in rock.

41 Ripple Marks Ripple marks are sand patterns formed by the action of wind, streams, waves, or currents. Ripple marks can be preserved when sand becomes sandstone.

42 Mud Cracks Mud cracks develop when deposits of wet clay dry and contract. The cracks fill in with different sediment and fossilize when the clay become shale.

43 Nodules Limestone and chalk often contain hard lumps of fine grained silica called nodules. Whitish, brown or gray nodules are called chert. Darker varieties are sometimes called flint. Throughout the ages, human have used these nodules for tools and weapons.

44 Concretions Round solid masses of calcium carbonate that form in layer of shale are called concretions. Concretions and nodules form when minerals in solution precipitate around a shell fragment or other impurity in clay sediment.

45 Geodes Limestone sometimes contains spheres of silica rock called geodes. Some geologist hypothesize that geodes form when groundwater creates cavities in the limestone. Minerals in the groundwater concentrate and grow in the cavities.

46 Metamorphic Rocks Metamorphic rocks are formed from preexisting rocks called “Parent Rocks”. The process by which a rock’s structure is changed by pressure, heat, and moisture is known as metamorphism. Rocks that undergo metamorphism can have a different internal structure, chemical composition, and texture than it’s parent rock.

47 Foliated vs. Non-Foliated
Foliated metamorphic rock has tendency to form bands of minerals or split along parallel layers. Non-foliated metamorphic rocks tend to fracture. Foliated Non-Foliated

48 Types of Metamorphism There are two main types of metamorphism:
Regional Metamorphism Local Metamorphism

49 Regional Metamorphism
Description of regional metamorphism: Occurs during mountain building Covers a large area Exposure to high heat and pressure When pressure is exerted greater in one direction, the minerals in the rock tend to align in layers.

50 Local Metamorphism When compared to regional metamorphism, contact metamorphism covers a much smaller area, usually less than 100 meters. There are two types of local metamorphism: Contact Metamorphism Deformational Metamorphism

51 Contact Metamorphism Contact metamorphism occurs when magma moves into rock, heating and changing it. Contact metamorphism fewer changes to the rock, in a much small area.

52 Deformational Metamorphism
Deformational metamorphism occurs at relatively low temperature but high pressure caused by stress and friction, most often at faults where rock masses pass each other. As the rock masses move, heat from friction, stress, and pressure cause the rock to deform.

53 Common Metamorphic Rocks
Sandstone Quartzite Shells Limestone Marble

54 Common Metamorphic Rocks
Shale Slate Phyllite Schist Granite Gneiss

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