MINERAL MIXTURES CHAPTER 2

Section 1 The Rock Cycle A rock is defined as a naturally occurring solid mixture of one or more minerals and organic matter The continual process by which new rock forms from old rock material is called the rock cycle

The value of Rock Early humans used as tools   Used for centuries to make buildings Granite, limestone, marble, sandstone, slate, etc. Modern buildings use concrete and plaster where rock is an important ingredient

Processes that Shape the Earth Weathering, Erosion, and Deposition The process in which water, wind, ice, and heat break down rock is called weathering. Weathering breaks rocks into fragments that become the sediment that are used to make sedimentary rocks

The process by which sediment is removed from its source is called erosion Water, wind, ice and gravity can erode and move sediments and cause them to collect

The process in which sediment moved by erosion is dropped and comes to rest is called deposition. Sediment is deposited in bodies of water and other low-lying areas and can be pressed and cemented together by minerals dissolved in water to form sedimentary rock.

Heat and Pressure Sedimentary rock made of sediment can also form when buried sediment is squeezed by the weight of overlying layers of sediment If the temperature and pressure are high enough at the bottom, the rock can change into metamorphic rock.   Sometimes the rock gets hot enough to melt, creating magma that eventually cools to form igneous rock

How the Cycle Continues Uplift is movement within the Earth that causes rocks inside the Earth to be moved to the Earth’s surface.

Buried rock is exposed at the Earth’s surface by a combination of uplift and erosion When uplifted rock reaches the Earth’s surface, weathering, erosion, and deposition begin.

Illustrating the rock cycle

Round and Round it Goes Each type of rock can change into one of the 3 types of rock This cycle, in which rock is changed by geological processes into different types of rock, is known as the rock cycle The location of rock determines which natural forces will have the biggest impact on the process of change

Rock Classification: Each rock type can be further divided depending on how it was formed. Composition: The minerals a rock contains determine the composition of that rock Texture: The size, shape, and positions of the grains that make up a rock determine a rock’s texture The texture of a rock can provide clues as to how and where the rock is formed

Section 2: Igneous Rock

Igneous rock forms when hot, liquid rock or magma, cools and solidifies The type of igneous rock that forms depends on the composition of the magma and the amount of time it takes the magma to cool.

Origins of igneous Rock Igneous rocks begin as magma. Magma forms in 3 ways: When rock is heated When pressure is released When rock changes composition

When magma cools enough, it solidifies to form igneous rock Liquid magma contains many melted minerals and these minerals have different melting points so magma will freeze or become solid before other minerals do.

Composition and Texture of igneous Rock Felsic Rocks – light colored rocks rich in elements such as aluminum, potassium, silicon, and sodium Granite Rhyolite

Mafic Rocks – Dark-colored rocks rich in calcium, iron, and magnesium, and poor in silicon Basalt

The longer it takes for the magma to cool, the more time the mineral crystals have to grow and therefore the larger the crystals are and the coarser the texture of the resulting igneous rock is. The less time it takes for the magma to cool, the less time the crystals have to grow so the rock being formed will be fine grained.

Igneous Rock formation Formations are located above and below the Earth’s surface

Intrusive Igneous Rock – when magma intrudes, or pushes, into surrounding rock below Earth’s surface and cools Usually coarse because it is insulated and cools slowly The minerals that form are large visible crystals

Plutons are large, irregular shaped intrusive bodies

Batholiths are the largest igneous intrusions

Stocks are intrusive bodies that are exposed over smaller areas than batholiths

Dikes are sheet-like intrusions that cut across previous rock units

Sills are sheet-like intrusions that are oriented parallel to previous rock units

Extrusive igneous Rock – igneous rock that forms from the magma that erupts, or extrudes, onto the Earth’s surface Common around volcanoes Cools quickly on the surface Contains very small or no crystals Sometimes lava flows from volcanoes Obsidian

Sometimes lava flows from cracks in the Earth’s surface called fissures Fissures in the ocean floor causes the creation of new ocean floor Large amounts of lava from fissures on land can cover a large area and form a plain called a lava plateau Pre-existing landforms are often buried by these lava flows.

Land Fissure

Ocean Fissure

The Giant’s Causeway is an area of 40,000 joined basalt columns which is a result of volcanic eruptions in the Paleocene. It is located in County Antrim on the northeast coast of Northern Ireland, near the city of Bushmills.

Section 3: Sedimentary Rock

Through the process of erosion sediments are moved from one place to another, eventually deposited in layers; older layers become compacted; dissolved minerals separate from water that passes through the sediment to form a natural cement that binds the rock and minerals together into sedimentary rock. Sedimentary rock forms at or near the Earth’s surface, without heat or pressure that is involved in metamorphic or igneous rocks The most noticeable feature of these rocks are the layers, or strata.

Composition of Sedimentary Rock Sedimentary rock is classified by the way it forms

Clastic sedimentary rock forms when rock or mineral fragments (clasts) are cemented together Can be coarse, medium or fine grained

Sandstone – Fine grained Conglomerate – Coarse grained Shale – Fine grained

Chemical Sedimentary rock forms when minerals crystallize out of a solution (like sea water) to become rock Example is Halite which forms when sodium ions and chlorine ions in shallow bodies of water become so concentrated that halite crystallizes from solution   Gypsum Halite

Organic Sedimentary Rock forms from the remains of once-living plants and animals Most Limestone forms from the fossils of ocean animals, such as coral or mollusks Coal is another of this type Coal Calcite

Sedimentary Rock Structures Stratification is the process in which sedimentary rocks are arranged in layers Strata differ from each other depending on the kind, size, and color of the sediment

Can record the motion of wind and water waves on lakes, oceans, rivers, and sand dunes in features called ripple marks Structures called mud cracks form when fine grained sediments at the bottom of a shallow body of water are exposed to the air and dry out

Section 4: Metamorphic Rocks Metamorphic rocks are rocks in which the structure, texture, or composition of the rock have changed, or gone through metamorphism.

Origins of Metamorphic Rock Form at 50 to 1,000 ⁰C, but some form at temperatures that are higher! It is the depth and pressure that the rock forms that allows it to heat up to this temperature and still remain a solid.

Two Types of Metamorphism: Contact metamorphism When rock is heated by nearby magma Some minerals in the surrounding rock are changed into other minerals by this increase in temperature Contact metamorphism occurs near igneous intrusions

Regional Metamorphism When pressure builds up in rock that is buried deep below other rock formations or when large pieces of the Earth’s crust collide with each other, regional metamorphism occurs Occurs over thousands of cubic kilometers deep within Earth’s crust Are found beneath most continental rock formations

Composition of Metamorphic Rock Index Minerals are certain minerals that only form at certain temperatures and pressures so they are used to estimate the temperature, depth, and pressure at which a rock undergoes metamorphism. They include: biotite mica, chlorite, garnet, kyanite, muscovite mica, sillimanite, and staurolite

2 Textures of metamorphic Rock: Foliated Mineral grains are arranged in plains or bands Usually contains aligned grains of flat minerals such as mica or chlorite

Nonfoliated The mineral grains are not arranged in planes or bands Commonly only made of one or only a few minerals During metamorphism, the crystals of these minerals may change in size or the minerals may change in composition in a process called recrystallization

Metamorphic Rock Structures Deformation is a change in the shape of a rock caused by a force placed on it. (these forces may cause a rock to be squeezed or stretched) Folds, or bends are structures that indicate that a rock has been deformed.