# Science: An Elementary Teacher’s Guide/Minerals, rocks, earthquakes, and erosion
## Minerals

A mineral is a naturally occurring substance, representable by a chemical formula, that is usually solid and inorganic, and has a crystal structure. It is different from a rock, which can be an aggregate of minerals or non-minerals and does not have a specific chemical composition. The exact definition of a mineral is under debate, especially with respect to the requirement a valid species be abiogenic, and to a lesser extent with regard to it having an ordered atomic study of minerals is called mineralogy.
The silicate minerals compose over 90% of the Earth's crust. The diversity and abundance of mineral species is controlled by the Earth's chemistry. Silicon and oxygen constitute approximately 75% of the Earth's crust, which translates directly into the predominance of silicate minerals. Minerals are distinguished by various chemical and physical properties. Differences in chemical composition and crystal structure distinguish various species, and these properties in turn are influenced by the mineral's geological environment of formation. Changes in the temperature, pressure, or bulk composition of a rock mass cause changes in its minerals.
Minerals can be described by various physical properties which relate to their chemical structure and composition. Common distinguishing characteristics include crystal structure and habit, hardness, lustre, diaphaneity, colour, streak, tenacity, cleavage, fracture, parting, and specific gravity. More specific tests for minerals include magnetism, taste or smell, radioactivity and reaction to acid.
The Rocks of the crust can me divided into three groups.
Sedimentary rock, they are made of layers of sediment that gather together on the earth's surface and are pressed together by pressure and chemicals. Igneous rock, forms of molten rock material, which is called magma. These two types of rocks are exposed to really high temperatures and pressures. Metamorphic rock, is a rock that has under gone a change.
Minerals are defined as solid, inorganic naturally compounds. Almost of all chemical elements of the earth, crust is associated with one mineral. Minerals grow in a wide variety of geological environments for example Deep Ocean, salt lakes, and volcanoes.

## Rocks and How They Form

In geology, rock or stone is a naturally occurring solid aggregate of one or more minerals or mineraloids. For example, the common rock granite is a combination of the quartz, feldspar and biotite minerals. The Earth's outer solid layer, the lithosphere, is made of rock.
Rocks have been used by mankind throughout history. From the Stone Age, rocks have been used for tools. The minerals and metals found in rocks have been essential to human civilization.
Three major groups of rocks are defined: igneous, sedimentary, and metamorphic. The scientific study of rocks is called petrology, which is an essential component of geology.
Igneous Rock
Forms through the cooling and solidification of magma or lava. This magma can be derived from partial melts of pre-existing rocks in either a planet's mantle or crust. Typically, the melting of rocks is caused by one or more of three processes: an increase in temperature, a decrease in pressure, or a change in composition.
Two Types of Igneous Rock
* Extrusive Rock: Formed from lava (Magma the reaches the Earth's Surface)
* Intrusive Rock: Formed from magma that cools and solidfies beneath the surface
Sedimentary Rock
Are formed at the earth's surface by the accumulation and cementation of fragments of earlier rocks, minerals, and organisms or as chemical precipitates and organic growths in water (sedimentation). This process causes clastic sediments (pieces of rock) or organic particles (detritus) to settle and accumulate, or for minerals to chemically precipitate (evaporite) from a solution. The particulate matter then undergoes compaction and cementation during at moderate temperatures and pressures (diagenesis).
Three types of Sedimentary Rocks
* Clastic Sedimentary Rock: Materials such as sand, gravel, silt, clay, cemented together; sandstone
* Biological Sedimentary Rock: Remains of plants or animals cemented together; Marine shells and coal.
* Chemical Sedimentary Rock: Chemicals dissolved in water that precipitate out; salt and limestone.
Metamorphic Rock
Are formed by subjecting any rock type—sedimentary rock, igneous rock or another older metamorphic rock—to different temperature and pressure conditions than those in which the original rock was formed. This process is called metamorphism; meaning to "change in form". The result is a profound change in physical properties and chemistry of the stone. The original rock, known as the protolith, transforms into other mineral types or other forms of the same minerals, by recrystallization.

## Earthquakes and How They Happen

An earthquake (also known as a quake, tremor or temblor) is the perceptible shaking of the surface of the Earth, resulting from the sudden release of energy in the Earth's crust that creates seismic waves. Earthquakes can be violent enough to toss people around and destroy whole cities. The seismicity or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time.
There are three main types of fault, all of which may cause an interplate earthquake: normal, reverse (thrust) and strike-slip.
Normal and reverse faulting are examples of dip-slip, where the displacement along the fault is in the direction of dip and movement on them involves a vertical component. Normal faults occur mainly in areas where the crust is being extended such as a divergent boundary. Reverse faults occur in areas where the crust is being shortened such as at a convergent boundary. Strike-slip faults are steep structures where the two sides of the fault slip horizontally past each other; transform boundaries are a particular type of strike-slip fault. Many earthquakes are caused by movement on faults that have components of both dip-slip and strike-slip; this is known as oblique slip.
Reverse faults, particularly those along convergent plate boundaries are associated with the most powerful earthquakes, megathrust earthquakes, including almost all of those of magnitude 8 or more. Strike-slip faults, particularly continental transforms, can produce major earthquakes up to about magnitude 8. Earthquakes associated with normal faults are generally less than magnitude 7. For every unit increase in magnitude, there is a roughly thirtyfold increase in the energy released.
Seismology is the scientific study of the seismic waves generated by earthquakes. Seismology is a young science, only about 150 years old. Before scientific studies began, ideas about earthquakes were largely based on myth and superstition. First seismograph in North America is installed at Lick Observatory near San Jose, California. This instrument will later record the 1906 San Francisco earthquake. Application of computers to larger datasets and problems begins in the 1960s: Routine earthquake locations Inverse problems Theoretical seismograms
Earthquakes caused by the shock waves created by shifting plates. These plates can interact in one of 3 ways:
* Convergent Movements When plates push into each other
* Divergent Movements When plates push away each other
* Transform Movements When plates slide by one another

## Erosion

In earth science, erosion is the action of surface processes (such as water flowing or wind blowing) that remove soil, rock, or dissolved material from one location on the Earth's crust, then transport it away to another location. Particulate breakdown of rock or soil into clastic sediment is referred to as physical or mechanical erosion; this contrasts with chemical erosion, where soil or rock material is removed from an area by its dissolving into a solvent (typically water), followed by the flow away of that solution. Eroded sediment or solutes may be transported just a few millimeters, or for thousands of kilometers. Erosion is the process that breaks things down. As far as we're concerned, erosion is the breakdown of the continents and the land around you. The overall effect of breaking down and weathering the land is called denudation. Denudation is the process of erosion. In nature, large things are broken down into smaller things. Boulders become sand. Mountains are rained on and become hills. The pieces of the mountain become smaller pieces and go down the sides of hills. Weathering and erosion always happen in a downhill direction. Erosion is an easy idea to understand. If you see a rock, pull it out of a mountain. Then throw it down on the ground. You are now a part of the erosion of that mountain. You have taken a big object (a mountain) and started to make little objects out of it (a rock). When that rock hit the ground, it could have cracked and made some tiny pieces of rock (sand). Erosion is just that easy. When it rains, the same process happens. Rocks are washed down a mountain or down a stream. Soils are washed away. The ocean beats against a cliff and breaks it apart. They are all examples of denudation.

## Rocks

The rocks of Earth's crust are classified into three groups according to their origin. Sedimentary rock are formed from sediments as materials in sand dunes and those that settle to the bottom of lakes and oceans. A sedimentary rock is formed from materials like gravel, sand, and clay carried by rivers and streams to lakes and oceans descend to the bottom and accumulate over long periods of time. One more type of sedimentary rock forms from the remains of plants and animals that live in the ocean. The third type of sedimentary rock includes chemicals such as salt and calcium carbonate these chemicals are deposited out of the water and accumulate on the ocean floor and eventually harden into rock. Igneous rock is formed from magma that comes from within Earth's surface. Extrusive rock cools so quickly that large crystals do not have time to form and extrusive rock is therefore usually glassy or made of very fine crystals. Intrusive rock have large, coarse crystals expected to the slow cooling of the magma. Metamorphic rock forms from igneous or sedimentary rock that has undergone a change in form due to extreme heat. Silicate Minerals Are those that contain the chemical element silicon. Nonmetallic Minerals This type of mineral contain metals such as calcium or magnesium. Metallic Minerals This type of mineral include gold, silver, copper, iron, lead, zinc, aluminum, mercury and titanium. Gem Minerals Are made into precious and semiprecious stones these include diamond, emerald, ruby, and topaz.