Download Minerals and Mineral Groups

Minerals and Mineral Groups
Say Thanks to the Authors
Click http://www.ck12.org/saythanks
(No sign in required)
To access a customizable version of this book, as well as other
interactive content, visit www.ck12.org
CK-12 Foundation is a non-profit organization with a mission to
reduce the cost of textbook materials for the K-12 market both
in the U.S. and worldwide. Using an open-content, web-based
collaborative model termed the FlexBook®, CK-12 intends to
pioneer the generation and distribution of high-quality educational
content that will serve both as core text as well as provide an
adaptive environment for learning, powered through the FlexBook
Platform®.
Copyright © 2015 CK-12 Foundation, www.ck12.org
The names “CK-12” and “CK12” and associated logos and the
terms “FlexBook®” and “FlexBook Platform®” (collectively
“CK-12 Marks”) are trademarks and service marks of CK-12
Foundation and are protected by federal, state, and international
laws.
Any form of reproduction of this book in any format or medium,
in whole or in sections must include the referral attribution link
http://www.ck12.org/saythanks (placed in a visible location) in
addition to the following terms.
Except as otherwise noted, all CK-12 Content (including CK-12
Curriculum Material) is made available to Users in accordance
with the Creative Commons Attribution-Non-Commercial 3.0
Unported (CC BY-NC 3.0) License (http://creativecommons.org/
licenses/by-nc/3.0/), as amended and updated by Creative Commons from time to time (the “CC License”), which is incorporated
herein by this reference.
Complete terms can be found at http://www.ck12.org/terms.
Printed: January 25, 2015
www.ck12.org
C HAPTER
Chapter 1. Minerals and Mineral Groups
1
Minerals and Mineral
Groups
Lesson Objectives
• Describe the characteristics that all minerals share.
• Identify the groups in which minerals are classified and their characteristics.
Vocabulary
•
•
•
•
•
chemical compound
crystal
inorganic
mineral
silicates
Introduction
Minerals are categorized based on their chemical composition. Owing to similarities in composition, minerals within
a same group may have similar characteristics.
What is a Mineral?
Minerals are everywhere! Figure 1.1 shows some common household items and the minerals used to make them.
The salt you sprinkle on food is the mineral halite. Silver in jewelry is also a mineral. Baseball bats and bicycle
frames both contain minerals. Although glass is not a mineral, it is produced from the mineral quartz. Scientists
have identified more than 4,000 minerals in Earth’s crust. A few are common, but many are uncommon.
Geologists have a very specific definition for minerals. A material is characterized as a mineral if it meets all of
the following traits. A mineral is an inorganic, crystalline solid. A mineral is formed through natural processes and
has a definite chemical composition. Minerals can be identified by their characteristic physical properties such as
crystalline structure, hardness, density, flammability, and color.
Crystalline Solid
Minerals are crystalline solids. A crystal is a solid in which the atoms are arranged in a regular, repeating pattern (
Figure 1.2). The pattern of atoms in different samples of the same mineral is the same. Is glass a mineral? Without
a crystalline structure, even natural glass is not a mineral.
1
www.ck12.org
FIGURE 1.1
Silver and halite are minerals; the mineral
quartz is used to make glass.
FIGURE 1.2
Sodium ions (purple balls) bond with chloride ions (green balls) to make
table salt (halite). All of the grains of salt that are in a salt shaker have this
crystalline structure.
Inorganic Substances
Organic substances are the carbon-based compounds made by living creatures and include proteins, carbohydrates,
and oils. Inorganic substances have a structure that is not characteristic of living bodies. Coal is made of plant and
animal remains. Is it a mineral? Coal is a classified as a sedimentary rock but is not a mineral.
Natural Processes
Minerals are made by natural processes, those that occur in or on Earth. A diamond created deep in Earth’s crust is
a mineral. Is a diamond created in a laboratory by placing carbon under high pressures a mineral? No. Do not buy a
laboratory-made “diamond” for jewelry without realizing it is not technically a mineral.
Chemical Composition
Nearly all (98.5%) of Earth’s crust is made up of only eight elements –oxygen, silicon, aluminum, iron, calcium,
sodium, potassium, and magnesium –and these are the elements that make up most minerals.
All minerals have a specific chemical composition. The mineral silver is made up of only silver atoms and diamond
is made only of carbon atoms, but most minerals are made up of chemical compounds. Each mineral has its own
chemical formula. Halite, pictured in the Figure 1.1, is NaCl (sodium chloride). Quartz is always made of two
2
www.ck12.org
Chapter 1. Minerals and Mineral Groups
oxygen atoms bonded to a silicon atom, SiO2 . If a mineral contains any other elements in its crystal structure, it’s
not quartz.
A hard mineral containing covalently bonded carbon is diamond, but a softer mineral that also contains calcium and
oxygen along with carbon is calcite ( Figure 1.3).
FIGURE 1.3
The structure of calcite shows the relationship of calcium (Ca), carbon (C),
and oxygen (O).
Some minerals have a range of chemical composition. Olivine always has silicon and oxygen as well as iron or
magnesium or both, (Mg, Fe)2 SiO4 .
Physical Properties
The physical properties of minerals include:
•
•
•
•
•
•
•
Color: the color of the mineral.
Streak: the color of the mineral’s powder.
Luster: the way light reflects off the mineral’s surface.
Specific gravity: how heavy the mineral is relative to the same volume of water.
Cleavage: the mineral’s tendency to break along flat surfaces.
Fracture: the pattern in which a mineral breaks.
Hardness: what minerals it can scratch and what minerals can scratch it.
How physical properties are used to identify minerals is described in the lesson on Mineral Formation.
Mineral Groups
Minerals are divided into groups based on chemical composition. Most minerals fit into one of eight mineral groups.
Silicate Minerals
The roughly 1,000 silicate minerals make up over 90% of Earth’s crust. Silicates are by far the largest mineral
group. Feldspar and quartz are the two most common silicate minerals. Both are extremely common rock-forming
minerals.
3
www.ck12.org
The basic building block for all silicate minerals is the silica tetrahedron, which is illustrated in Figure 1.4. To
create the wide variety of silicate minerals, this pyramid-shaped structure is often bound to other elements, such as
calcium, iron, and magnesium.
FIGURE 1.4
One silicon atom bonds to four oxygen
atoms to form a silica tetrahedron.
Silica tetrahedrons combine together in six different ways to create different types of silicates ( Figure 1.5). Tetrahedrons can stand alone, form connected circles called rings, link into single and double chains, form large flat sheets
of pyramids, or join in three dimensions.
FIGURE 1.5
The different ways that silica tetrahedrons can join together cause these two minerals to look very different.
4
www.ck12.org
Chapter 1. Minerals and Mineral Groups
Native Elements
Native elements contain atoms of only one type of element. Only a small number of minerals are found in this
category. Some of the minerals in this group are rare and valuable. Gold, silver, sulfur, and diamond are examples
of native elements.
Carbonates
The basic carbonate structure is one carbon atom bonded to three oxygen atoms. Carbonates include other elements,
such as calcium, iron, and copper. Calcite (CaCO3 ) is the most common carbonate mineral ( Figure 1.6).
FIGURE 1.6
Calcite is the most common carbonate
mineral.
Azurite and malachite, shown in the Figure 1.7, are carbonates that contain copper instead of calcium.
FIGURE 1.7
Two carbonate minerals: (a) deep blue azurite and (b) opaque green malachite.
5
www.ck12.org
Halides
Halide minerals are salts that form when salt water evaporates. Halite is a halide mineral, but table salt is not the
only halide. The chemical elements known as the halogens (fluorine, chlorine, bromine, or iodine) bond with various
metallic atoms to make halide minerals (see Figure 1.8).
FIGURE 1.8
Fluorite is a halide containing calcium and
fluorine.
Oxides
Oxides contain one or two metal elements combined with oxygen. Many important metals are found as oxides.
Hematite (Fe2 O3 ), with two iron atoms to three oxygen atoms, and magnetite (Fe3 O4 ) ( Figure 1.9), with three iron
atoms to four oxygen atoms, are both iron oxides.
FIGURE 1.9
Magnetite is the most magnetic mineral.
Magnetite attracts or repels other magnets.
6
www.ck12.org
Chapter 1. Minerals and Mineral Groups
Phosphates
Phosphate minerals are similar in atomic structure to the silicate minerals. In the phosphates, phosphorus, arsenic,
or vanadium bond to oxygen to form a tetrahedra. There are many different minerals in the phosphate group, but
most are rare ( Figure 1.10).
FIGURE 1.10
Turquoise is a phosphate mineral containing copper, aluminum, and phosphorus.
Sulfates
Sulfate minerals contain sulfur atoms bonded to oxygen atoms. Like halides, they form where salt water evaporates.
The sulfate group contains many different minerals, but only a few are common.
Gypsum is a common sulfate with a variety of appearances ( Figure 1.11). Some gigantic 11-meter gypsum crystals
have been found. That is about as long as a school bus!
Sulfides
Sulfides are formed when metallic elements combine with sulfur. Unlike sulfates, sulfides do not contain oxygen.
Pyrite, or iron sulfide, is a common sulfide mineral known as fool’s gold. People may mistake pyrite for gold because
the two minerals are shiny, metallic, and yellow in color.
Lesson Summary
• For a substance to be a mineral, it must be a naturally occurring, inorganic, crystalline solid that has a
characteristic chemical composition and crystal structure.
• The atoms in minerals are arranged in regular, repeating patterns that can be used to identify that mineral.
• Minerals are divided into groups based on their chemical composition.
• The chemical feature of each groups is: native elements –only one element; silicates –silica tetrahedron;
phosphates –phosphate tetrahedron; carbonates –one carbon atom with three oxygen atoms; halides –a halogen
7
www.ck12.org
FIGURE 1.11
Although the orange crystals on the left looks nothing like the white sands on the right, both the crystals and
sands are gypsum.
bonded with a metallic atom; oxides –a metal combined with oxygen; sulfates –sulfur and oxygen; sulfides
–metal with sulfur, no oxygen.
Review Questions
1. What is a crystal?
2. Which elements do all silicate minerals contain?
3. Obsidian is a glass that forms when lava cools so quickly that the atoms do not have a chance to arrange
themselves in crystals. Is obsidian a crystal? Explain your reasoning.
4. What are the eight major mineral groups?
5. What is the same about all minerals in the silicate group? What is different about them?
6. One sample has a chemical composition with a ratio of two iron atoms to three oxygen atoms. Another
sample has a chemical composition with a ratio of three iron atoms to four oxygen atoms. They contain the
same elements: Are they the same mineral?
7. How does the native elements mineral group differ from all of the other mineral groups?
8. On a trip to the natural history museum you find two minerals that are similar in color. You can see from
their chemical formulas that one mineral contains the elements zinc, carbon, and oxygen. The other mineral
contains the elements zinc, silicon, oxygen, and hydrogen. Your friend tells you that the minerals are in the
same mineral group. Do you agree? Explain your reasoning.
Further Reading / Supplemental Links
• The Definition of a Mineral: http://www.minsocam.org/msa/ima/ima98(04).pdf .
• Mineral Identification: http://geology.csupomona.edu/alert/mineral/minerals.htm .
• Dana Classification of Minerals: http://webmineral.com/danaclass.shtml .
8
www.ck12.org
Chapter 1. Minerals and Mineral Groups
• A Lot of Different Minerals: http://hyperphysics.phy-astr.gsu.edu/hbase/geophys/mineral.html#c1 .
• Mineral Groups: http://mineral.galleries.com/minerals/silicate/class.htm .
• Giant Crystal Cave, National Geographic: http://news.nationalgeographic.com/news/2007/04/photogalleries/g
iant-crystals-cave/photo3.html .
Points to Consider
•
•
•
•
Why is obsidian, a natural glass that forms from cooling lava, not a mineral?
Why are diamonds made in a laboratory not minerals?
Is coal, formed mostly from decayed plants, a mineral? Is it a rock?
Artists used to grind up the mineral azurite to make colorful pigments for paints. Is the powdered azurite still
crystalline?
References
1. Necklace: Flickr:Tikanchay handcrafted jewelry from Peru; Salt mill: User:ElinorD/Wikimedia Commons;
Glass: Will Murray (User:Willscrlt/Wikimedia Commons); Silver: Courtesy of US Geological Survey and
Mineral Information Institute; Salt: Courtesy of US Geological Survey and Mineral Information Institute;
Quartz: Courtesy of Ken Hammond/US Department of Agriculture. Necklace: http://www.flickr.com/phot
os/29874248@N06/2811981846/; Salt mill: http://commons.wikimedia.org/wiki/File:Saltmill.jpg; Glass:
http://commons.wikimedia.org/wiki/File:Highball_Glass_%28Tumbler%29.svg; Silver: http://commons.wiki
media.org/wiki/File:SilverUSGOV.jpg; Salt: http://commons.wikimedia.org/wiki/File:ImgSalt.jpg; Quartz: h
ttp://commons.wikimedia.org/wiki/File:USDA_Mineral_Quartz_Crystal_93c3951.jpg . Necklace: CC BY
2.0; Rest: Public Domain
2. Ben Mills (User:Benjah-bmm27/Wikimedia Commons). http://commons.wikimedia.org/wiki/File:Sodium-ch
loride-3D-ionic.png . Public Domain
3. Zachary Wilson. CK-12 Foundation . CC BY-NC 3.0
4. CK-12 Foundation. CK-12 Foundation . CC BY-NC 3.0
5. (a) Kevin Walsh; (b) Image copyright Manamana, 2014. (a) http://www.flickr.com/photos/86624586@N00/68
51318708/; (b) http://www.shutterstock.com . (a) CC BY 2.0; (b) Used under license from Shutterstock.com
6. (a) Ben Mills (User:Benjah-bmm27/Wikimedia Commons); (b) Ed Uthman. (a) http://commons.wikimedia
.org/wiki/File:Carbonate-3D-balls.png; (b) http://www.flickr.com/photos/euthman/4739088809/ . (a) Public
Domain; (b) CC BY 2.0
7. (a) Parent Géry; (b) User:Alkivar/Wikipedia. (a) http://commons.wikimedia.org/wiki/File:Azurite_cristalli
s%C3%A9e_%28Chine%29_3_.jpg; (b) http://commons.wikimedia.org/wiki/File:MoreMalachite.jpg . Public Domain
8. Bruce. Fluorite . CC BY 2.0
9. User:Parent Géry/Wikimedia Commons. http://commons.wikimedia.org/wiki/File:Magn%C3%A9tite_1_%28B
olivie%29.jpg . Public Domain
10. Stephanie Clifford (Flickr:sdixclifford). http://www.flickr.com/photos/30486689@N08/2932194265/ . CC
BY 2.0
11. Left: Dave Dyet; Right: Rob Pongsajapan; Composite created by CK-12 Foundation. Left: http://com
mons.wikimedia.org/wiki/File:Actinolite_3170.jpg; Right: http://www.flickr.com/photos/pong/5281844989/
. Left: Public Domain; Right: CC BY 2.0
9