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Mineral Groups
Dana Desonie, Ph.D.
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Printed: September 9, 2014
AUTHOR
Dana Desonie, Ph.D.
www.ck12.org
C HAPTER
Chapter 1. Mineral Groups
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Mineral Groups
• Describe the characteristics of mineral groups.
How could a mineral crystal grow as big as two giraffes?
The crystals in Giant Crystal Cave in Mexico measure up to 36 feet long. How could minerals grow that big? Beyond
requiring many years, the environment was completely suited for crystal growth, with lots of space, a perfect 136o F
temperature and lots of mineral-rich water.
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.
The basic building block for all silicate minerals is the silica tetrahedron, which is illustrated in Figure 1.1. To
create the wide variety of silicate minerals, this pyramid-shaped structure is often bound to other elements, such as
calcium, iron, and magnesium.
Silica tetrahedrons combine together in six different ways to create different types of silicates ( Figure 1.2). 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.
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 ( Figure 1.3), silver, sulfur, and diamond
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FIGURE 1.1
One silicon atom bonds to four oxygen
atoms to form a silica tetrahedron.
FIGURE 1.2
The different ways that silica tetrahedrons can join together cause these two minerals to look very different.
are examples of native elements.
Carbonates
The basic carbonate structure is one carbon atom bonded to three oxygen atoms. Carbonates consists of some cation
(like C, Fe, Cu, Mg, Ba, Sr, Pb) bonded to a carbonate molecule. Calcite (CaCO3 ) is the most common carbonate
mineral ( Figure 1.4).
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Chapter 1. Mineral Groups
FIGURE 1.3
A gold nugget.
FIGURE 1.4
Calcite.
Halides
Halide minerals are salts that form when salt water evaporates. Halite is a halide mineral, but table salt (see Figure
1.6) 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. All halides are ionic minerals, which means that they are
typically soluble in water.
Oxides
Oxides contain one or two metal elements combined with oxygen. Many important metal ores are oxides. Hematite
(Fe2 O3 ), with two iron atoms to three oxygen atoms, and magnetite (Fe3 O4 ) ( Figure 1.7), with three iron atoms to
four oxygen atoms, are both iron oxides.
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FIGURE 1.5
Two carbonate minerals: (a) deep blue azurite and (b) opaque green malachite. Azurite and malachite are
carbonates that contain copper instead of calcium.
FIGURE 1.6
Beautiful halite crystal.
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Chapter 1. Mineral Groups
FIGURE 1.7
Magnetite is one of the most distinctive
oxides since it is magnetic.
Phosphates
Phosphate minerals are similar in atomic structure to the silicate minerals. In the phosphates, phosphorus bonds
to oxygen to form a tetrahedron. As a mineral group they aren’t particularly common or important rock-forming
minerals, but they are important for you and I. Apatite ( Figure 1.8) is a phosphate (Ca5 (PO4 )3 (F,OH)) and is one of
the major components of human bone!
FIGURE 1.8
Apatite.
Sulfates
Sulfate minerals contain sulfur atoms bonded to four oxygen atoms, just like silicates and phosphates. Like halides,
they form where salt water evaporates. The most common sulfate mineral is probably gypsum (CaSO4 (OH)2 ) (
Figure 1.9). Some gigantic 11-meter gypsum crystals have been found (See opening image). That is about as long
as a school bus!
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FIGURE 1.9
Gypsum.
Sulfides
Sulfides are formed when metallic elements combine with sulfur in the absence of oxygen. Pyrite ( Figure 1.10)
(FeS2 ) is a common sulfide mineral colloquially known as "fool’s gold" because it has a golden metallic looking
mineral. There are three easy ways to discriminate real gold from fools gold: real gold is extremely dense, real gold
does not grow into perfect cubes, as pyrite commonly does, and pyrite smells like rotten eggs (because of the sulfur).
FIGURE 1.10
This mineral has shiny, gold, cubic crystals with striations, so it is pyrite.
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Chapter 1. Mineral Groups
Summary
• Silicates, made of building blocks of silica tetrahedrons, are the most abundant minerals on Earth.
• Silica tetrahedrons combine together in six different ways to create rings, single and double chains, large flat
sheets, or 3-dimensional structures.
• Other mineral groups have other anions like carbonates, oxides, or phosphates.
• Minerals that are native elements are made of only one element.
Explore More
Use this resource to answer the questions that follow.
Introduction to Minerals, start at 6:40 https://www.youtube.com/watch?v=ahRTRV8l70c
1. What mineral group is 96% of Earth’s crust made of? What are the two most common examples of this mineral
group?
2. What are the halides and what are the common ions that create them, the anions (negatively charged) and
cations (positively charged)?
3. What do all carbonates contain? If the cation is copper, what is the mineral?
4. What do all sulfates contain? Which sulfate is sheet rock made of?
5. What do all sulfides contain? What other element does pyrite contain?
6. What do all oxides contain? If an aluminum oxide is blue what is it?
7. What is the characteristic of native elements? Name Au, Cu, S, C
Review
1. What is the most common group of minerals on Earth? What do they all contain?
2. How are the silicates categorized?
3. Your friend brings you a fist-sized perfect cube of a golden mineral, which he tells you is gold. What should
you and your friend consider before determining that he is right?
References
1. CK-12 Foundation. One silicon atom bonds to four oxygen atoms to form a silica tetrahedron. CC BY-NC 3.0
2. (a) Kevin Walsh; (b) Image copyright Manamana, 2014. Muscovite and tourmaline are both silicates, but their
tetrahedrons join together in different ways. (a) CC BY 2.0; (b) Used under license from Shutterstock.com
3. Chris Ralph (User:Reno Chris/Wikipedia). A gold nugget. Public Domain
4. User:Alkivar/Wikipedia. A calcite crystal. Public Domain
5. (a) Parent Géry; (b) User:Alkivar/Wikipedia. Azurite and malachite are both carbonate minerals. Public
Domain
6. Chris Ralph (User:Reno Chris/Wikipedia). A halite crystal. Public Domain
7. User:Parent Géry/Wikimedia Commons. A crystal of magnetite, which is magnetic. Public Domain
8. User:OG59/Wikimedia Commons. Apatite is a phosphate mineral. Public Domain
9. Courtesy of United States Geological Survey and the Mineral Information Institute. Gypsum is a sulfate
mineral. Public Domain
10. Flickr:pnjunction2007. Pyrite, fool’s gold, is a sulfide mineral. CC BY 2.0
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