Rock Cycle and Minerals From Old Red-Diamond Book p. s92-s105 & Buckle Down Mississippi.

Rock Cycle and Minerals

From Old Red-Diamond Book p. s92-s105

&

Buckle Down Mississippi

Rocks and the Rock Cycle

Studies of the Earth Show that it was once made mostly of molten materials.

As the Earth cooled, the materials at the Earth’s surface solidified into the first rocks.

The first rocks and all others that form when magma cools are called igneous rocks.


Over time weathering and erosion breaks down rock materials

This weathered rock material or sediment can eventually stick back together.


Sedimentary rocks form from pieces of rock that were broken up by weathering processes

Deposits of these pieces then stick together or lithify, by compaction or cementation.


Heat and pressure inside the Earth can change both igneous and sedimentary rocks into metamorphic rocks.

Sometimes the minerals in the rocks are rearranged into a different pattern

In other cases, entirely new minerals are formed.


The formation of igneous, sedimentary, and metamorphic rocks are the individual steps of an endless process that has been going on for billions of years.

Old rocks are constantly being made into new rocks by a continuous process called the rock cycle.


Rock Cycle defined: The continuous process of change in which new rocks are formed from old rock material.

Rocks and the Rock CycleEXAMPLE: When you consider the rock cycle

remember that every rock on Earth has been through the cycle numerous times.

When Magma cools, for example, it may form the igneous rock granite.

Granite can then broken down by physical and chemical weathering into particles such as sand

Rocks and the Rock CycleEXAMPLE: Deposits of this sand can be cemented

into a sedimentary rock called sandstone.

If this sandstone becomes buried deep within the earth and is exposed to heat and pressure it can be changed into the metamorphic rock called quartzite.

Rocks and the Rock CycleEXAMPLE: Finally, quartzite may later be forced

even deeper into the earth where can be remelted to become magma once more and restart the whole process.


Is this the only pathway for a rock to travel through the rock cycle? ---NO---

Suppose granite is not broken down into sand, but exposed to high temperatures and extreme pressures.

In this case, the granite could become a metamorphic rock gneiss.

The granite itself may also be remelted to form magma.

Rock Forming Minerals As Magma and Lava cool, the chemical

compounds that make up molten rock link together to for crystals of certain minerals.

Minerals are solids made from inorganic (non-living) processes

Each type of mineral has a specific crystal structure and chemical composition.

Minerals are usually made up of two or more chemical elements

Rock Forming Minerals

Kinds of Minerals The Earth’s crust contains over 2000

different minerals, Only about 20 of these minerals are very

common. These are the basic rock forming minerals

of the Earth’s crust.

All minerals can be classified into two categories based on their chemical composition. Silicates

Non Silicates

Kinds of Minerals

Kinds of Minerals

Silicates

Silicon and oxygen are the two most common elements in the Earth’s crust.

Minerals that contain silicon and oxygen are called silicates.

Silicate minerals make up about 96% of the earth’s crust

Examples of Silicates

A common silicate mineral that you might be familiar with is quartz.

A crystal of quartz is composed of single silicon atoms, each bonded to 4 oxygen atoms.

These atoms form a network in the shape of a tetrahedron, which is a three- sided pyramid.

Feldspars are the most abundant silicate materials.

In addition to silicon and oxygen they contain aluminum and calcium, potassium or sodium atoms in their crystals.

Examples of Silicates

Non-Silicates

Only 4% of the earth’s crust is composed of non-silicate minerals.

There are several different families of these minerals based on their chemical composition.

One of the most important families of nonsilicate minerals are the Carbonates.

For example- Calcite (calcium carbonate) which makes

up limestone. Dolomite

Non-Silicates

Non-Silicates Other mineral families are characterized

by different chemical groups Oxides contain oxygen

bonded to an element other than silicon ex. iron oxide (magnetite)

Halides contain halogen ex. Halite and Fluorite.

Sulfides contain sulfur ex. Galena and Pyrite

Some nonsilicate minerals contain only one kind of element. These rare minerals are called Native Elements.

Many of the minerals in this group are valuable metals. Some examples are gold, silver, and copper.

Non-Silicates- Native Elements

Nickel and Iron may also appear as native elements, but they are rare in the earth’s crust.

However much of the interior of the earth is believed to consist of uncombined nickel and iron.

Non-Silicates Native Elements

Diamond and Graphite are also native elements because they are made of pure carbon.

They differ only in the way carbon atoms are arranged.

Non-Silicates Native Elements

Identifying Properties of Minerals We’ve said that every type of mineral

has a specific crystal structure and chemical composition, but

Some minerals look very much alike. How can geologists tell similar-looking

minerals apart?

Identifying Properties of Minerals Geologists can tell

similar-looking minerals apart by comparing their physical properties

Color Luster Streak Hardness Cleavage

Identifying Properties of Minerals- Color Many minerals have bright colors. For

example,

Cinnabar is red

Azurite is deep blue

Serpentine is green,

Sulfur is bright yellow

Unfortunately, color is one of the least dependable characteristics you can use to identify a mineral.

The color of many minerals is due to the presence of small amounts of other elements called impurities.

For examples pure quartz is colorless, but with impurities it can be pink, tan, red, purple, or black.

Identifying Properties of Minerals- Color

The shine of a newly waxed car is its luster or the way it reflects light.

The luster of minerals also refers to the appearance of its surface in reflected light.

Identifying Properties of Minerals- Luster

Each mineral has a characteristic luster.

Some of the terms used to describe luster --- metallic, glassy, waxy, pearly, greasy, earthy ---are related to familiar objects.

Identifying Properties of Minerals- Luster

Some minerals leave a mark when rubbed on a rough surface. (like chalk on a sidewalk)

The color of the powder in these marks is called the mineral’s streak.

Identifying Properties of Minerals- Streak

Identifying Properties of Minerals- Streak Sometimes the color of the streak is different

from the color of the mineral sample.

The streak of golden colored pyrite is greenish-black.

And the streak of silver colored hematite is brick-red.

Another characteristic of minerals is their hardness or resistance to being scratched.

Moh’s Scale of Mineral Hardness is a set of ten standard minerals that is used to compare the hardness of all minerals.

Identifying Properties of Minerals- Hardness

Moh’s Scale lists 10 minerals from 1 (softest) to 10 (hardest).

A Mineral with a greater number can always scratch a mineral with a lesser number.


If a certain mineral can scratch a penny its hardness is greater than 3.

If a steel nail can scratch it, you know its hardness is less than 5.

Using the hardness scale if a mineral easily scratches glass it must have hardness greater than 6.


Cleavage and fracture are terms that describe how minerals break.

Minerals that always break along flat surfaces have a property called cleavage.

These minerals have a characteristic crystal shape that is due to the arrangement of the atoms that make up the mineral.

Identifying Properties of Minerals- Cleavage

Identifying Properties of Minerals- Cleavage The cleavage of a particular mineral always

occurs in the same way and produces crystal faces that have characteristic angles.

Halite, for example breaks into cubes ,

while calcite pieces tilt diagonally

and mica peels off in thin sheets.

If a mineral does not have cleavage, but breaks into irregular pieces this pattern of breaking is called fracture.

This is similar to breaking glass. Quartz and obsidian break this way.

Identifying Properties of Minerals- Fracture

Identifying Properties of Minerals- Special propertiesSome minerals show other interesting

characteristics, for example:Magnetite is a type of iron oxide that is magnetic.

Pitchblende, which contains uranium, is radio-active.

Calcite gives off light when exposed to UV light or X rays, this property is called fluorescence.

Some minerals continue to glow after the UV light is removed. This property is called phosphorescence.

Identifying Properties of Minerals- Special properties

Identifying Properties of Minerals- Special properties

Identifying Properties of Minerals- Special properties Calcite, in addition to fluorescence also:

Will have a chemical reaction to hydrochloric acid and begin to bubble &

A very clear calcite crystal will exhibit double refraction (you can see two images of what you are looking at through the clear calcite).

Rock Cycle and Minerals From Old Red-Diamond Book p. s92-s105 & Buckle Down Mississippi.

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Transcript of Rock Cycle and Minerals From Old Red-Diamond Book p. s92-s105 & Buckle Down Mississippi.