G-116 Week 2
Minerals and the Chemistry of the Earth
Click
on the link below to hear a mini-lecture audio segment.
G-116 Week 2
Minerals and the Chemistry of the Earth
Click
on the link below to hear a mini-lecture audio segment.
The Composition of the Earth
The Earth is composed of various types of building blocks.One way of looking at the composition of the Earth is to look at the spectrum of materials.Ions ---- Molecules ---- Minerals ---- RocksIons and atoms are the smallest subdivision we commonly use for earth materials.Ions and atoms are single elements (like oxygen or hydrogen) that are composed of a nucleus containing protons and neutrons, and shells of electrons around them. An atom has a balanced or neutral charge and an ion has a positive or negative charge.
Molecules are groups of ions bonded together to form a chemical compound. Water is an example of a molecule. An individual molecule may not be stable on it own, but can become a stable substance when a number of molecules are present...like water or plastics.
Molecules formed when ions are bonded. There are a number of types of bonds, however, the most common bonds in earth materials are ionic and covalent bonding.
Ionic bonding occurs when two atoms of opposite charge are attracted to each other, as demonstrated in the link below.
Covalent bonding occurs when two atoms share an electron in their outer shells, as demonstrated in the link below.
When a group of ions or molecules form a solid structure, called a lattice, a mineral compound may form. The lattice shown below is from the silicate minerals group.
A 3-dimensional panorama of the silicate structure shown above can be viewed in the link below.
Put on you 3D glasses and click the links below. This link is an object movie. Place the cursor in the middle of the image, hold the mouse down and move the cursor across the image.
A mineral is defined as a naturally occurring, crystalline, inorganic material with a specific range of chemical composition and an regular internal order of atoms.
Another type of lattice structure is shown in the link below.
Minerals form all of the major materials on the surface of the Earth.Minerals ...... Rocks ....... Soil ...... Sediment
The Formation of MineralsMinerals form by crystallization from a molten liquid or from water. Some minerals form when a molten magma cools. As the magma reaches its characteristic temperature, it crystallizes. Other minerals form by precipitation from water, either by evaporation (like the mineral halite) or by precipitation from an aqueous solution (like calcite). The mineral forms in a regular and predictable fashion that is related to its internal structure and composition.
The mineral crystal is the outward expression of the internal chemistry and order of a mineral, as shown in the virtual reality object movie in the link below.
The Chemical Nature of the EarthThe chemical composition of the minerals on Earth reflects the overall chemical composition of the Earth.What elements would you expect to find in a random mineral specimen you picked up from the ground?
Lets look at the major mineral groups and see if they reflect the chemical compositions above.
The Mineral Groups
The Silicates
The silicate minerals re the most abundant mineral on earth, and are often referred to as the "rock forming" minerals. Silicates are formed from the basic building block of the silicate ion (SiO4), shown below. Click the link below to see examples of this mineral group.
The Carbonates
The carbonate minerals are the most abundant non-silicate mineral group. Calcite (CaCO3) is the most common carbonate mineral and is the major constituent of the rock limestone. Click the link below to see examples of this mineral group.
The Sulfides
The chief ores of many of the valuable industrial minerals, such as copper, zinc, and nickel are members of the sulfide group. The sulfide minerals all include the sulfide ion (S -2). Click the link below to see examples of this mineral group.
The Oxides
The oxide minerals are compounds in which oxygen is bonded to atoms or cations of other minerals such as iron. Click the link below to see examples of this mineral group.
To see the common rock forming minerals, put on you 3D glasses and click the link below.
Minerals and Rocks
The Physical Properties of Minerals
In order to fully understand the nature and identity of rocks, it is important to be able to identify the individual minerals contained in a rock. To identify minerals geologists rely on the chemical and physical properties that are easy to observe or measure.
Color is not a terribly useful property because many minerals display the same colors and some minerals display several colors. Click the link below to learn more about this property.
Density is the weight of a mineral per unit volume. Click the link below to explore the concept of density.
Luster is the way in which light is reflected by light. It can be useful when combined with other physical properties to identify an unknown mineral. Click the link below to explore the concept of density.
The crystal form of a crystal is the geometric shape it assumes when crystallized. Click the links below to explore the concept of density.
The best way to understand crystal form is to look at a crystal in 3D.A 3D object movie of a rhombohedral calcite movie is linked below. This link is an object movie. Place the cursor in the middle of the image, hold the mouse down and move the cursor across the image.Calcite Rhombohedron Object Movie
You may also wish to look at a mineral structure without the 3D glasses, in the link below. This link is an object movie. Place the cursor in the middle of the image, hold the mouse down and move the cursor across the image.
The cleavage of a mineral is the manner in which it parts along a plane or system of planes. Some minerals display fracture instead of cleavage. Cleavage is a useful property.
The hardness of a mineral is its ability to resist abrasion. The hardness of a mineral is measured with a scale called the Moh's hardness scale, and is shown below.
Click the link below to learn more about hardness.
Special Properties
In some cases minerals display special properties that help us identify them. Among these are streak and acid reaction.
Some minerals have the property of streak, which is a variation between the color of the mineral and its powder. The mineral Hematitie is shown below. It is greay but has a blood red powder when scraped against a ceramic plate.
Another special property of some minerals is their chemical reaction with acid. Calcite, for example fizzes violently when exposed to hydrochloric acid (HCl).
In the laboratory this week, you will learn to identify minerals by measuring their physical properties. In the exercises below, you will measure the physical properties and identify several unknown mineral specimens.
Some minerals are extremely important from a commercial point of view. Such minerals are called "industrial minerals" and they represent an important economic sensor. Such minerals as gold and silver are obvious examples of minerals of economic importance, however, there are other minerals that are less glamourous, but very useful. The mineral gypsum, for example, is extremely important to the building trades. The wallboards in your house are composed of gypsum and plaster. Companies and individuals have spent countless hours and huge amounts of money trying to find deposits of economic minerals.
Some of the important economic minerals are shown in the table below.
Gold has historically been the measure of wealth. Before World War II most countries backed their currency with gold stockpiled in mints and forts. The gold rush of 1848-9 in California was one of the major historical events in America in the 19th century and led to the settlement of the west. In this exercise you will search for gold. Click the link below to access this exercise.
Rocks and their Mineral Constituents
We must often identify rocks by determining the minerals of which the rock is composed. Thus, mineral identification is an important component in rock identification. In the two exercises below we will use our mineral identification skills.
Sometimes we can tell from examining a rock that, based on what minerals contituents it has, it might be one type of rock or another.
