Presentation on theme: "A rock is a naturally occurring solid mixture composed of minerals, smaller rock fragments, organic material, or glass. The individual particles in a."— Presentation transcript:
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.
There three main types of rocks: 1. Igneous 2. Sedimentary 3. Metamorphic
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: 1. Felsic 2. Intermediate 3. Mafic 4. Ultramafic
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.
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.
There are two main types of igneous rock: 1. Intrusive 2. Extrusive
Intrusive igneous rocks form below the Earth’s surface and cool slowly. Characteristics of Intrusive igneous rock include: 1. Course texture 2. Large grains 3. Large crystals. 4. Light-colored
Extrusive igneous rock forms when lava cools and crystallizes on the Earth’s surface. Characteristics of extrusive igneous rock include: 1. Fine texture 2. Small grains 3. Small crystals. 4. Dark-colored
Igneous rock is classified into three families: 1. Granite Family 2. Gabbro Family 3. Diorite 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.
PropertiesGraniteObsidianPumice Color Salmon, gray, black Smoky brownLight gray Luster Dull with some pearly and glassy GlassyDull Hardness StreakNo streak or whiteWhite BreakFractureConchoidalFracture Density2.6 – 2.7 g/cm g/cm 3.64 g/cm 3 Specific Gravity Crystal StructureAnhedralNone Special Properties-Floats
Granite Obsidian Pumice
Igneous rock forms from mafic magma. These rocks are dark in color, fine grained and denser than rock in the granite family.
Properties ScoriaOlivineBasalt Color Reddish BrownGreenish BlackBlack, Dark gray Luster Glassy Dull Hardness Streak Reddish brownWhiteBlack Break FractureConchoidalFracture Density 2.6 g/cm g/cm 3 3 g/cm 3 Specific Gravity.8 – – Crystal Structure NoneOrthorhombicNone Special Properties -
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.
Properties DioriteAndesite Color Black, White, Salt and Pepper Gray with black crystals Luster Glassy Hardness Streak Bluish blackWhite Break CleavageConchoidal Density 2.7 g/cm – 2.8 g/cm 3 Specific Gravity – 3.4 Crystal Structure NoneOrthorhombic Special Properties -
Ultramafic rocks consist of mainly mafic minerals that are dark in color, coarse grain and dense. Rocks in this family include: Peridotite Dunite Pyroxenite
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.
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.
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.
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.
The process of forming a sedimentary rock is known as “Lithification”. There are three main processes of lithification: 1. Clastic Process 2. Chemical Process 3. Organic 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”
Conglomerate Breccia Sandstone Shale
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
Organic sedimentary rock forms from sediment containing the remains of plants and animals. Common organic sedimentary rocks are limestone and coal.
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.
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.
Peat Lignite Bituminous Anthracite
Fossils: Fossils are the remains, impressions, and any other evidence of plants or animals preserved in rock.
Ripple marks are sand patterns formed by the action of wind, streams, waves, or currents. Ripple marks can be preserved when sand becomes sandstone.
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.
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.
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.
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.
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.
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
There are two main types of metamorphism: 1. Regional Metamorphism 2. Local Metamorphism
Description of regional metamorphism: 1. Occurs during mountain building 2. Covers a large area 3. Exposure to high heat and pressure 4. When pressure is exerted greater in one direction, the minerals in the rock tend to align in layers.
When compared to regional metamorphism, contact metamorphism covers a much smaller area, usually less than 100 meters. There are two types of local metamorphism: 1. Contact Metamorphism 2. Deformational 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.
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.