Content Benchmark E.8.C.6
Students know minerals have different properties and different distributions according to how
they form. E/S
If it can’t be grown, it has to be mined is the slogan for the Mineral Information Institute, an
organization which provides information and materials to teachers and students that result in an
understanding that mineral and energy resources are essential to society and are produced in an
environmentally and socially responsible manner (accessed at http://www.mii.org/). Everything
we use in our daily life originates from our natural resources. Often students’ associate minerals
with vitamins, but to a geologist the meaning of the word mineral is quite different. By
definition, a mineral is a naturally formed, inorganic solid having a specific chemical
composition and characteristic crystal structure.
Variety of Minerals
There are approximately 4000 varieties of minerals which can be classified into one of eight
major mineral classes similar to how biologists classify living organisms into groups such as
plants, animals, fungi, and bacteria.
Interactive Chart of Minerals, click on any underlined link to see a sample of the mineral.
Silicate Oxide
Carbonate Sulfide
Sulfate
Halide Hydroxide Phosphate
Native
Elem.
fluorite limonite
graphite
tourmaline magnetite siderite
pyrite
barite
staurolite
hematite
galena
anhydrite halite
garnet
corundum azurite
chalcopyrite gypsum
olivine
bauxite
sphalerite
augite
hornblende
biotite
chlorite
asbestos<>
epidote
sillimanite
orthoclase
plagioclase
quartz
kyanite
kaolinite
muscovite
talc
malachite
dolomite
calcite
apatite
sulpher
Figure 1. Interactive Chart of Minerals.
(From http://www.auburn.edu/~leeming/mineral.html)
Mineral Classification
Minerals, however, are classified into groups by their composition and crystal structure. Ninety
five percent of the rocks found in Earth’s crust contain minerals known as silicates. Silicates are
the most abundant minerals and make up about 25% of all known minerals. The structure of all
silicates is based on a silicon atom surrounded by four oxygen atoms. Silicates can be further
classified into six subclasses differentiated by their structure. Common silicates include quartz,
feldspars, pyroxene and olivine.
Figure 2. Common Silicate minerals.
(From http://www.indiana.edu/~geol116/week2/images_pages/silicates.html)
Three fourths (75%) of known minerals are non-silicates. These remaining minerals are grouped
mainly by their chemical composition. Minerals formed when metals, like iron and aluminum,
bond with oxygen are known as oxides such as hematite, corundum, magnetite, and rutile. Many
oxides form by the weathering of other minerals. Corundum (AlO2) is best known for its gem
forms: ruby and sapphire.
Figure 3. Common Oxide mineral samples.
(From http://www.indiana.edu/~geol116/week2/images_pages/oxides.html)
Sulfides also contain metals, but instead of oxygen, they combine with one or two sulfur atoms.
The most abundant sulfide in Earth’s crust is pyrite, also known as “fool’s gold.”
Figure 4. Iron Pyrite sample
(From http://www.3dchem.com/imagesofmolecules/pyrite2.jpg)
Compared to a sample of crystalline gold (Figure 5) it is easy to see why pyrite (Figure 4) has “fooled”
many people into thinking they have “struck it rich” when in actuality they have found a mineral of little
value.
Figure 5. Crystalline gold sample.
(From http://www.webmineral.com/specimens/Gold.jpg )
Sulfides include many ores which can occur in large deposits with economic value. Ores are
rocks that contain enough metal or valuable minerals to make them worth mining. The
concentration of metal determines its value. Ores containing iron, such as galena, must contain
more than 50% to be economically valuable, whereas ores containing silver or platinum may
only require 0.01% in order to be valuable. Other common sulfides are sphalerite, a zinc ore, and
chalcopyrite, an ore containing both copper and iron.
Another group of non-silicate minerals are the halides. Table salt, sodium chloride (NaCl), is the
most common halide, known as Halite. Halides dissolve easily in water and are often soft and
transparent.
Figure 6. Halide Mineral Sample of Fluorite (CaF2).
(From http://www.fluoritesite.com/gallery/fluorite-detail08.jpg)
Carbonates, Phosphates, and Sulfates make up the remaining mineral groups composed of
chemical compounds. Despite what their name implies Phosphates may or may not contain
phosphorus. Regardless of their name, some contain arsenic, vanadium, or antimony. Similarly,
sulfates do not all contain sulfur. They can contain chromium, tungsten, selenium, or
molybdenum. Common sulfates include gypsum, barite, and anhydrite.
Figure 7. Gypsum Starburst, a common sulfate mineral, in a not so common form.
(From http://www.rockhounds.com/rockshop/gypsum.jpg)
Carbonates are the most extensive group aside from silicates and phosphates. They are minerals
consisting of metals and the carbonate (CO3)2- ion. These minerals are further classified by their
crystal structure into calcite, aragonite, and dolomite. Calcite is the most abundant carbonate
mineral.
Figure 8. Calcite and Dolomite two common carbonate minerals.
(From http://www.indiana.edu/~geol116/week2/images_pages/carbonates.html )
Although most minerals are formed by chemicals combined in various compounds, others exist
simply as elements in their pure form. These minerals are called native elements and are made
up entirely of the same types of atoms. Copper, gold, lead, nickel, iron, and diamonds are all
examples of the elemental form of minerals.
Figure 9. Pure gold sample.
(From http://www.lehighminerals.com/World100plus1.htm)
Figure 10. A sample of pure copper.
(From http://www.caltelephone.com/lamps/new_page_4.htm)
Mineral Identification
With all these thousands of minerals, how can geologist tell them apart? There are simplified
methods of identification that can be done in the field using simple equipment like a rock
hammer, scale and/or a hand-lens. Other identification methods are more elaborate and are
commonly done in a laboratory setting utilizing high powered microscopes or chemical analysis.
Just as you can typically spot your best friend in a crowd of people, often times a geologist can
identify a mineral simply by looking at the sample. Sometimes, however, it is easier to identify
an individual if it they are separated from the group. Geologist can separate a mineral from the
rock it is found in by using their rock hammer, as they do so they note how the mineral breaks
apart. Different minerals have different breakage patterns the pattern or way the mineral breaks
in known as cleavage. Mica, for example, tends to break neatly into thin sheets, whereas a
mineral with poor cleavage, like quartz, may break into jagged/angular pieces.
Hardness
Attempting to scratch the mineral sample with the nail or even another known mineral can also
provide clues to the identifying factor known as hardness. Friedrich Mohs invented his famous
scale for determining mineral hardness back in 1822, when asked to organize the mineral
collection of a wealthy Austrian banker. The scale ranks minerals from 1 the softest (talc) to 10
the hardest (diamond).
Figure 11. Mohs Hardness Scale showing minerals at each hardness level.
(From http://stloe.most.go.th/html/lo_index/LOcanada2/203/4_en.htm)
Crystal Structure
Upon close inspection, the shape of the individual mineral crystals may be noted. Crystals form
patterns and each mineral type possesses its own specific pattern. There are seven crystalline
systems that can be used to help identify a mineral sample: cubic, tetragonal, rhombic, trigonal,
hexagonal, monoclinic and triclinic.
Figure 12. Crystal Structures Diagram
(From http://invsee.asu.edu/nmodules/spheresmod/density.html)
The crystalline structure can help identify the mineral, but not necessarily the element itself. For
example, the element carbon can be found as both diamond and graphite.
Figure 13. Diamond and Graphite comparison. Although both are
made from pure carbon, one is the hardest substance
known to man the other is one of the softest.
(From http://commons.wikimedia.org/wiki/Image:Diamond_and_graphite.jpg)
Density
Density of the sample can also be used as an identifying factor. By finding the displaced volume
and mass of an unknown sample, the density (D = M/V) can be calculated. This ratio, known as
specific gravity, can be compared to complied tables containing values for known minerals to
assist in identification.
NONMETALLIC MINERALS
HARDNESS (9 - 1)
FRACTURE
CLEAVAGE
fracture,
sometimes
with parting
LUSTER
DIAPHANEITY
vitreous
to
adamantine
transparent,
transluscent
fracture
vitreous
fracture
conchoidal
fracture
vitreous
to
resinous
vitreous
to
greasy
transparent,
to
opaque
transparent,
to
opaque
transparent
to
transluscent
transparent
to
transluscent
conchoidal
fracture
vitreous
fracture
dull
opaque
fracture
dull
transluscent,
opaque
fracture
dull earthy
transluscent,
opaque
OTHER
PROPERTIES
sometimes has
hexagonal
crystals
sometimes
striations
SPECIFIC
GRAVITY
MINERAL
NAME
4.02
CORUNDUM
3.02 - 3.2
TOURMALINE
3.5 - 4.3
GARNET
sometimes
isometric
crystals
sometimes has
hexagonal
crystals
frequently
as granular
masses
sometimes
oolitic or
magnetic
earthy
color and
appearance
2.65
QUARTZ
3.27 - 4.27
OLIVINE
5.26
HEMATITE
2.7 - 4.3
LIMONITE
pisolitic
2.00 - 2.55
BAUXITE
By: Art Crossman
Mineralogy / Petrology (1997)
Figure 14. Sample Mineral Identification Chart, Including Specific Gravity
(From http://geology.com/minerals/mineral-identification.shtml )
Color
Color can also be used as an identifying characteristic, but it is often unreliable due to impurities
or weathering. Quartz, for example, can be found in its pure state as clear and colorless, but it
can also be found in various colors ranging from violet, pink, green, and even black.
Figure 15. Various Quartz Samples.
(From http://oldweb.uwp.edu/academic/geology/workshop/images3/quartz2.jpg)
A more reliable test utilizing color is the streak test. This can be performed by scratching a
mineral against a rough unglazed piece of ceramic or porcelain tile. The color of the powder or
streak remaining on the plate is typically the same for all samples of a specific mineral. It can
also be used to tell two similarly looking samples apart. Gold and pyrite are both golden color
minerals, but their streak immediately distinguishes them. Gold produces a golden streak, but
pyrite produces a dark green-black streak. Galena and hematite can also be easily confused
because of their similar dull gray color. When tested on a streak plate galena reveals the same
dull gray color, but hematite produces a clearly identifiable blood-red streak.
Figure 16. Streak plate comparison of hematite and pyrite.
(From http://www.theimage.com/geology/notes3/streakplate.jpg)
Luster
Geologist may also observe the sample’s luster – the way the mineral reflects and refracts light.
Typically luster is described as metallic or non-metallic. Non-metallic lusters can be further
described as greasy, shinny, glassy, or earthy.
Figure 18. Examples of the various types of mineral luster.
(From http://csmres.jmu.edu/geollab/fichter/Minerals/luster.html)
How Minerals Form
There are two main ways in which minerals form; either by the crystallization of materials
dissolved in water or through crystallization of melted materials. The easiest way for crystals to
develop is through the evaporation of water. For example, halite, gypsum, and calcite can all
form from the evaporation of seawater. The crystal size depends on the rate of evaporation, with
large crystals resulting from slow evaporation, whereas, quick evaporation leads to smaller
crystals.
Figure 19. The Bonneville Salt Flats of Utah contain halite formed by evaporation
(From http://bp0.blogger.com/_m3lKiZKA9kw/R1XmlzzKeeI/AAAAAAAAAYA/6Vz2nhXqfNc/s1600h/bonneville-salt-flats4.jpg)
In addition to seawater, elements that form minerals can also dissolve in hot water that is often
found near magma instructions, and form a solution. When this hot solution cools, the elements
and compounds crystallize and form new minerals. Pure metals that crystallize underground
often form narrow channels or slabs of minerals known as veins. These veins often contain
valuable ores such as hematite, gold, silver, and galena
When molten rock cools, atoms also bond together into mineral crystals. Minerals form as hot
magma cools inside the crust or when lava hardens on the Earth’s surface. The size of the
crystals depends on the rate of cooling. Slow cooling leads to large crystals. Magma closer to the
surface loses heat energy much faster than magma that hardens deep below the ground, therefore,
the lava cools quickly and smaller crystals result
Bowen’s Reaction Series
Figure 20. Bowen’s Reaction series shows minerals formation at various temperatures
(From http://www.physicalgeography.net/fundamentals/10e.html)
Content Benchmark E.8.C.6
Students know minerals have different properties and different distributions according to how
they form. E/S
Common misconceptions associated with this benchmark
1. Students have difficulty understanding the definition of a mineral.
Students often believe rocks and minerals are the same thing. They believe humans can
fabricate rocks and minerals. In addition, they believe minerals are not important to their
lives.
For more information about these misconceptions and for strategies to address them, visit the
Common Misconceptions about Rocks and Minerals website at
http://onramp.nsdl.org/eserv/onramp:1144/sept08_pl_m.html
What Is It? An interactive activity can be used to assess prior knowledge can be accessed at
http://www.contentclips.com/services/getPresenterHtml?uri=:cli:79
What Is It? Directions and answer key is found at
http://onramp.nsdl.org/eserv/onramp:1227/what_is_it_answer_key.pdf
2. The Source of Student Misconceptions about Rock Formation
In depth research article that analyzes narrative essays - stories of rock formation - written by
pre-service elementary school teachers.
To access the full article, GROWING PEBBLES AND CONCEPTUAL PRISMS –
UNDERSTANDING THE SOURCE OF STUDENT MISCONCEPTIONS ABOUT ROCK
FORMATION, use the following link
http://www.nagt.org/files/nagt/jge/abstracts/Kusnick_v50n1p31.pdf
Content Benchmark E.8.C.6
Students know minerals have different properties and different distributions according to how
they form. E/S
Sample Test Questions
Content Benchmark E.8.C.6
Students know minerals have different properties and different distributions according to how
they form. E/S
Answers to Sample Test Questions
Content Benchmark E.8.C.6
Students know minerals have different properties and different distributions according to how
they form. E/S
Intervention Strategies and Resources
The following is a list of intervention strategies and resources that will facilitate student
understanding of this benchmark.
1. The Mineral Information Institute – free teaching materials.
MII site resource that contains packets to download or a form to fill in and receive
information by mail. Here you will find Everyday Uses of Minerals, the Every American
Born Will Need Poster, along with links to Homework Help for Students.
The MII home page is located at
http://www.mii.org/aboutmii.php#programs
2. Women in Mining Education Foundation
Classifying Minerals Activity which contains student worksheet and instructions for
completion, can be found at
http://www.womeninmining.org/activities/classifying_minerals.pdf
3. Mineral Matters from San Diego Natural History Museum
This site offers some practical advice on how to identify minerals, how to turn the pile of
rocks and minerals “you” have collected into an organized rock and mineral collection, as
well as other practical advice for the those new to mineral and rock collecting.
This site and its activities can be accessed by visiting
http://www.sdnhm.org/kids/minerals/index.html
4. Minerals Management Service Pacific Region
The Minerals Management Service Pacific Region has a long-standing commitment to work
with local educators and students to improve access to scientific information and to increase
interest in and an understanding of math and science.
This site can be accessed by visiting,
http://www.mms.gov/omm/pacific/kids/teachers.htm
5. 3D Images of Common Minerals
Indiana University created a fun 3D image gallery. Note: 3D glasses are recommended for
viewing.
These images can be viewed at,
http://www.indiana.edu/~geol116/week2/3dmineral/3dmin.html
6. Specific Gravity Test
An online activity that can be used by students to determine the amount of gold in a nugget
that contains other material such as quartz.
This activity and explanation can be viewed at,
http://home.att.net/~desert-gold-diggers/gold/specgrav.htm
7. The Life Cycle of a Mineral Deposit
A Teacher’s Guide for Hands-On Mineral Education Activities. Download this free teacher’s
guide and supporting materials at
http://pubs.usgs.gov/gip/2005/17/
8. USGS Minerals Information
Find publications of "Minerals Yearbook" 1994-2005 for the state of Nevada. Website also
includes links to the Nevada Bureau of Mines & Geology, the Association of American State
Geologists, USGS Fact Sheets-Nevada, and USGS Geological Research Activities- Nevada.
http://minerals.usgs.gov/minerals/pubs/state/nv.html
9. Webminerals listing of Minerals A-Z
A wealth of information containing details of over 4000 minerals. Each page contains
information on the mineral’s chemical formula, composition, crystallography, locality, name
origin, physical properties, and includes images.
http://webmineral.com/Alphabetical_Listing.shtml