Download Minerals: Physical Properties - Mr. Kieffer: Grade 8 Earth Space

Minerals: Physical Properties
EARTH/SPACE SYSTEMS
EARTH MATERIALS AND PROCESSES UNIT
MINERALS SUB-UNIT
1. A mineral occurs naturally.
2. A mineral is solid.
3. A mineral has a definite chemical
composition.
4. A mineral’s atoms are arranged in an orderly
pattern.
5. A mineral is inorganic (was never alive)
Of the almost 4000 known
minerals, only about 30 are
common.
The most common are
quartz,feldspar,mica, and calcite.
These minerals make up most of the
rocks found in the Earth’s crust.
How do geologists classify minerals?
 Identified about 3,800 minerals
 Each has characteristic properties that can be used to
identify it
 What do you predict some of those characteristic
properties might include?
Video clip on Rocks and Minerals
 Why do we “care” about minerals?
 How do they impact our daily lives?
 http://www.youtube.com/watch?v=9cHUbyaid1k
COLOR
 Easily observed physical property
 Often too little information to make identification
 Can only be used to identify minerals that always have
own characteristic color
Examples:
- Gold, Pyrite, and Chalcopyrite all have gold color, so you
need additional information to identify these minerals
- Malachite is always green
Action! Arrange your minerals by color
 How did your group arrange the minerals?
 Was arranging them by color easy or difficult?
 What considerations did you need to make?
 Were there any minerals that you found difficult to
place by color? Why?
Streak of a mineral is the color of its
powder when rubbed on an
unglazed white tile.
The streak is often not the same
color as the mineral.
A minerals color may vary, but the
streak rarely will!
STREAK
 To do this test, rub the mineral across a piece of
unglazed porcelain tile and see what color the
powder is
Examples:
- Pyrite has a gold color but a greenish black streak
- Gold has a gold color and a golden yellow streak
Action! Streak Test
 Use the unglazed tile and try the streak test on your
minerals.
 Which mineral left a streak that was the same color
as your mineral?
 Which mineral left a streak that was a different color
than the mineral?
 Was there anything about running this test that your
group had difficulty doing?
Luster refers to the way a mineral
shines in reflected light.
Notice the difference between
these two minerals?
The mineral on the left has a
metallic luster, the one on the
right, a nonmetallic luster.
There are several terms used to
describe nonmetallic luster.
Examples could be vitreous, like the
quartz on the left, or pearly, like the
gypsum on the right.
Other terms that might be used include
greasy, dull, and earthy.
Can you tell which of these has an
earthy luster and which has a vitreous
luster?
Vitreous
Earthy
LUSTER
Examples:
- Galena is an ore of lead, and has a bright, metallic
luster
- Quartz has a glassy luster
Action! Identify the luster of your minerals.
 Look on page 117 (red) or 123 (orange) in Inside
Earth textbook.
 Identify the luster for each of your minerals.
- How did your group classify mineral 1?
- How did your group classify mineral 2?
- How did your group classify mineral 3?
- How did your group classify mineral 4?
- How did your group classify mineral 5?
 Did your group have trouble identifying the luster for
any of these minerals?
DENSITY
 Each mineral has a characteristic density.
 Density is the mass in a given space, or mass per unit
volume.
 You can “heft” or feel a mineral’ weight by picking
two mineral samples up and comparing their weight.
 How do you think geologists could precisely measure
the mass of a mineral sample?
Measuring Density
 Geologists measure density by using a balance to
determine the mineral sample’s mass, and then by
placing the mineral in water and determining how
much water was displaced.
 The volume of water displaced equals the volume of
the sample.
 Dividing the sample’s mass by its volume gives the
density of the mineral.
 Density = mass/ volume
Density Problem
 If a sample of Olivine has a mass 237 grams and a
volume of 72 ml (cm3), then the density will be
- 237 g/ 72 cm3 = 3.3 g/cm3
Now your turn! A sample of Calcite has a mass of 324
grams and a volume of 120 ml (cm3).
What is its density?
320 grams / 120 cm3 = 2.7 g/ cm3
HARDNESS
 One of the best clues when identifying minerals
 In 1812, Friedrich Mohs developed the “Mohs
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hardess scale” to describe the hardness of minerals
Ranks ten minerals from softest to hardest
Can be determined by a “scratch test”
A mineral can scratch any mineral softer than itself,
and can be scratched by a mineral that is harder.
Which of these minerals do you think is the softest?
Quartz, Diamond, or Talc
Mohs Hardness Scale
Talc = 1
 The softest know mineral
 Talc flakes when scratched by a fingernail
 Used as a powder on people’s skin
Gypsum = 2
 A fingernail can easily scratch it!
 Used in plaster, shampoo, hair products, and foot
creams
Calcite = 3
 A fingernail can’t scratch it, but a penny can!
 One of the most common elements on Earth
 Primary mineral in cave formations
 Also most sea shells are composed of calcite
 Pulls carbon dioxide out of sea and thus functions as
a filter for Earth
 Will fix and dissolve when in an acidic solution
 Used in construction: limestone, marble
 Also in paint, animal feed, and as a cleaner
Fluorite = 4
 A steel knife can easily scratch this mineral.
 Is used in aluminum, on dishes that can go in the
oven, in telescopes and lenses, and for ornamental
uses
Apatite = 5
 A steel knife can scratch this mineral as well, though
not as easily as Fluorite.
 Used commonly in fertilizers
Feldspar = 6
 It can’t be scratched by a steel knife, but it can
scratch window glass.
 Used in ceramics and cleaners
 Most abundant mineral found in Earth’s crust
Quartz = 7
 It can easily scratch steel and hard glass.
 Second most abundant mineral found in Earth’s
continental crust
 making of sandpaper, optics, glass, circuit boards,
computer components, cement , mortar, and jewelry.
 Time can be measured from the vibrations of the
quartz crystals so quartz crystals are often used in
clocks.
Topaz = 8
 It can scratch quartz.
 Most common use is as a gemstone in jewelry.
Corundum = 9
 Used as an abrasive
Diamond = 10
 Mostly use as gemstones but also used in
semiconductors, cutting, grinding, and drilling
 Hardest mineral
Action! Run hardness tests on your minerals.
 Use the penny and steel nail to arrange your
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minerals from softest to hardest.
Look on p. 122 (orange) or 118 and 119 (red) to
determine where each mineral might fall on the
Mohs hardness scale.
Where did you classify mineral 1?
Where did you classify mineral 2
Where did you classify mineral 3?
Where did you classify mineral 4?
Where did you classify mineral 5?
Crystal shape can be a useful
property to identify minerals if the
minerals have had the time and
space to form crystals. Most
mineral grains that are found in
rocks, lack the room to grow.
Crystal Systems
- Crystals of each mineral grow atom by atom to form
that mineral’s crystal structure
- Geologists classify minerals into six groups based on
the number and angle of the crystal faces.
 Look in Inside Earth on p. 124 (orange) or pp. 120 121 (red).
 What is the crystal system of quartz called? What is
its density?
 What is the crystal system of Magnetite? What is its
density?
 What is the crystal system of quartz called?
Hexagonal
 What is its density?
2.6
g/cm3
 What is the crystal system of Magnetite?
Cubic
 What is its density?
 5.2 g/cm3
The cleavage of a mineral is its
tendency to split easily or to
separate along flat surfaces.
Cleavage can even be observed on
tiny mineral grains making it a very
useful property!
Cleavage
 This is determined by how the atoms in its crystal are
arranged.
 This arrangement causes the mineral to break apart
more easily in one direction than in another.
Example: Mica is probably the best
example as it splits into thin sheets.
It is said to have one perfect
cleavage.
Fracture
 “Fracture” describes how a mineral looks when it is
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broken apart in an irregular way.
Geologists use many terms to describe this
characteristic; including
“shell-shaped” when it breaks and leaves a surface
that looks like a seashell
“hackly” when pure metals, such as copper and iron
break, and form jagged points.
“earthy” when soft minerals crumble like clay
Special Properties
 Look at p. 126 (orange)and p. 122 (red) to find
examples of each of these special properties Magnetism: has properties of magnets
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Magnetite or Lodestone
 Fluorescence: glows under ultraviolet light
 Scheelite
 Optical properties: bends light
 Calcite
 Reactivity: reacts chemically
 Calcite, Aragonite
Special Properties Examples