minerals: physical properties
DESCRIPTION
Minerals: Physical Properties. EARTH/SPACE SYSTEMS EARTH MATERIALS AND PROCESSES UNIT MINERALS SUB-UNIT. Mineral Characteristics. 1. A mineral occurs naturally. 2. A mineral is solid. 3. A mineral has a definite chemical composition. - PowerPoint PPT PresentationTRANSCRIPT
EARTH/SPACE SYSTEMS
EARTH MATERIALS AND PROCESSES UNIT
MINERALS SUB-UNIT
Minerals: Physical Properties
Of the almost 4000 known minerals, only about 30 are common.
The most common are quartz,feldspar,mica, and calcite.
How do geologists classify minerals?
Identified about 3,800 mineralsEach has characteristic properties that can
be used to identify itWhat 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=9cHUbyaid
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COLOR
Easily observed physical propertyOften too little information to make identificationCan 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?
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?
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?
Earthy
Vitreous
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?
HARDNESS
One of the best clues when identifying mineralsIn 1812, Friedrich Mohs developed the “Mohs
hardess scale” to describe the hardness of mineralsRanks ten minerals from softest to hardestCan 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
Talc = 1
The softest know mineralTalc flakes when scratched by a fingernailUsed 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 EarthPrimary mineral in cave formationsAlso most sea shells are composed of calcitePulls carbon dioxide out of sea and thus
functions as a filter for EarthWill fix and dissolve when in an acidic solutionUsed in construction: limestone, marbleAlso 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 cleanersMost 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 crustmaking 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.
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 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 2Where 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 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 Magnetite or Lodestone
Fluorescence: glows under ultraviolet light Scheelite
Optical properties: bends light Calcite
Reactivity: reacts chemically Calcite, Aragonite