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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.

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minerals physical properties

Minerals: Physical Properties

EARTH/SPACE SYSTEMS

EARTH MATERIALS AND PROCESSES UNIT

MINERALS SUB-UNIT

slide2

Mineral

Characteristics

slide8
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
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
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
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
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?
slide14

streak

Streak of a mineral is the color of its powder when rubbed on an unglazed white tile.

slide15

streak

The streak is often not the same color as the mineral.

A minerals color may vary, but the streak rarely will!

streak
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
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?
slide18

luster

Luster refers to the way a mineral shines in reflected light.

Notice the difference between these two minerals?

slide19

luster

The mineral on the left has a metallic luster, the one on the right, a nonmetallic luster.

slide20

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.

slide21
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?

Were you

Right?

Vitreous

Earthy

luster
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
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
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
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
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
HARDNESS
  • One of the best clues when identifying minerals
  • In 1812, Friedrich Mohs developed the “Mohs 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

talc 1
Talc = 1
  • The softest know mineral
  • Talc flakes when scratched by a fingernail
  • Used as a powder on people’s skin
gypsum 2
Gypsum = 2
  • A fingernail can easily scratch it!
  • Used in plaster, shampoo, hair products, and foot creams
calcite 3
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
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
Apatite = 5
  • A steel knife can scratch this mineral as well, though not as easily as Fluorite.
  • Used commonly in fertilizers
feldspar 6
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
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
Topaz = 8
  • It can scratch quartz.
  • Most common use is as a gemstone in jewelry.
corundum 9
Corundum = 9
  • Used as an abrasive
diamond 10
Diamond = 10
  • Mostly use as gemstones but also used in semiconductors, cutting, grinding, and drilling
  • Hardest mineral
action run hardness tests on your minerals
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 2
  • Where did you classify mineral 3?
  • Where did you classify mineral 4?
  • Where did you classify mineral 5?
slide41

crystal shapes

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
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?
slide43

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
slide44

cleavage

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
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.
slide46

cleavage

Example: Mica is probably the best example as it splits into thin sheets. It is said to have one perfect cleavage.

fracture
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
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
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