Chapter 4: Minerals

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Chapter 4 Minerals

• Section 1 Properties of Minerals

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Key Concepts

• What is a mineral?
• How are minerals identified?

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What is a Mineral?

• mineral A naturally occurring, inorganic solid
  that has a crystal structure and a definite
  chemical composition.
• A substance must have all 5 characteristics to be
  classified as a mineral.

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5 Characteristics of a Mineral

• A mineral must be/have
• Naturally Occurring
• Inorganic
• Solid
• Crystal Structure
• Definite Chemical Composition

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Naturally occurring means

• The substance must be formed by processes that
  occur naturally in the world
• Example quartz
• Forms naturally when magma cools and hardens deep
  beneath the Earths surface.

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NOT naturally occurring

• Materials such as cement, plastic, brick, steel,
  and glass all come from substances found in
  Earths crust but they are manufactured by people.

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Inorganic

• Inorganic the mineral cannot arise from
  materials that were once part of a living thing
• Ex. Coal is NOT a mineral because it is made up
  the remains of plants and animals

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Solid

• A mineral is always solid
• Has a definite volume and shape.
• Particles that make up a solid are tightly packed
  together, therefore they move very little
  (compared to the particles of a liquid)

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Crystal Structure

• Particles of the mineral line up in a pattern
  that repeats.
• The repeating pattern of the minerals particles
  forms a solid called a crystal
• Faces are flats sides of the crystal that meet
  at sharp edges and corners

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QUICK REVIEW What Is the Difference Between an
Element and a Compound?

• Element a substance composed of a single kind
  of atom.
• Ex. Hydrogen
• Compound Two or more elements combined so that
  the elements no longer have distinct properties
• Ex. Water H20

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Definite Chemical Composition

• Minerals always contain certain elements in
  definite proportions most minerals are compounds
• example Quartz
• SiO2
• One element of silicon, 2 elements of oxygen
• Compounds have their own unique properties that
  differ from the properties of the elements that
  form it.

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Definite Chemical Composition

• Some elements that occur in nature, in pure form,
  that are minerals include
• Gold (Au), Silver (Ag), Copper (Cu)
• Listed on the periodic table

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Identifying Minerals

• Geologists have identified about 3,800 minerals
• Each mineral has characteristic properties that
  can be used to identify it.
• Some properties can be determined by looking at
  it, some properties require testing.

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Identifying Properties

• Color
• Streak
• Luster
• Density
• Hardness
• Crystal Systems
• Cleavage and fracture
• Special Properties

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Identifying Property- Color

• An easily observed physical property.
• Color alone is not enough to make an
  identification.
• Ex. Gold, pyrite and chalcopyrite gold color
• Only a few minerals can be identified using color
  only.
• Ex. Malachite- always green, azurite always
  blue.

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Identifying Property - Streak

• The streak of a mineral is the color of its
  powder
• The streak color and the mineral color are often
  different
• To test rub a mineral against an unglazed tile
  (streak plate)

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Identifying Property - Luster

• Luster used to describe how a mineral reflects
  light from its surface.
• Minerals containing metals are often shiny.
• Other terms to describe luster - Earthy, waxy,
  and pearly.

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Identifying Property - Density

• Each mineral has a characteristic Density.
• Density the mass in a given space or mass per
  unit volume.
• Density mass (g)
• volume (cm3)
• Displacement the volume of the displaced water
  equals the volume of the sample

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Calculating Density
- Properties of Minerals

• To calculate the density of a mineral, divide the
  mass of the mineral sample by its volume.
• Density Mass/Volume
• For example, if a sample of olivine has a mass of
  237 g and a volume of 72 cm3, then the density is
• 237 g/72 cm3 3.3 g/cm3

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Stop and Think

• Take a few minutes to work through the following
  problem with a partner.

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Practice Problem

• A sample of calcite has a mass of 324 g and a
  volume of 120 cm3. What is its density?

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Answer

• 324 g 120 cm3 2.7 g/cm3

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Stop and Think

• Take a few minutes to work through the following
  problem with a partner.

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Mineral Density
- Properties of Minerals

• Predicting
• A piece of pyrite has a volume of 40 cm3. What
  is its mass?

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Mineral Density
200 g
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Stop and Think

• Take a few minutes to work through the following
  problem with a partner.

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Analyzing Data

1. What is the mass of sample B? What is the volume
   of sample B?
2. What is the density of Sample B?
3. What is the mass of Sample C? What is the
   volume of Sample C?
4. What is the density of Sample C?
5. Compare the density of Sample B to that of Sample
   C?

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Answers

• 1) 50g and 10cm3
• 2) 5g/cm3
• 3) 100g and 20cm3
• 4) 5g/cm3

• 5) the density of samples B and C is the same.

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Identifying Property - Hardness

• Friedrich Mohs An Austrian mineral expert.
• In 1812 invented a test to describe the hardness
  of minerals.
• Called the Mohs hardness scale
• This scale ranks minerals from softest to hardest
• A scratch test is used, a mineral can scratch any
  mineral softer than itself, but can be scratched
  by any mineral that is harder.

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Identifying Property - Hardness
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Identifying Property Crystal Systems

• The crystals of each mineral grow atom by atom to
  form the minerals crystal structure.
• Geologists classify these structures into 6
  groups based on the number and angle of the
  crystal faces.
• These groups are called crystal systems.
• Example- Halite crystals are cubic. Halite
  crystals have 6 square faces that meet at right
  angles forming a perfect cube.

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- Properties of Minerals
Identifying Property Crystal Systems
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Crystal systems cleavage and fracture

• Cleavage a property of a mineral that causes it
  to split easily along flat surfaces.
• Determined by the arrangement of atoms in its
  crystals.
• The arrangement of the atoms in the mineral
  causes the crystal to break apart more easily in
  one direction than another.
• Example- Mica separates easily in only one
  direction, forming flat sheets. Feldspar is
  another mineral that has cleavage.

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Cleavage
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Crystal Systems cleavage and fracture

• Fracture describes how a mineral looks when it
  breaks apart in an irregular way.
• Most minerals do not split apart evenly.

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• Geologist use a variety of terms to describe
  fracture
• Examples quartz has a shell shaped (conchoidal)
  fracture. When it breaks, it produces curved,
  shell like surfaces that look like chipped glass.
• Pure metals like copper and iron form jagged
  points - hackly (jagged) fracture.
• soft minerals that crumble - earthy fracture
• Minerals that form rough, irregular surfaces -
  uneven fracture

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Conchoidal Fracture

• Smooth and curved (called clam shell too)

Quartz (SiO2 , Silicon dioxide )
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Subconchoidal Fracture

• Subconchoidal Smooth and but not curved

Andalusite (Al2 SiO5, Aluminum Silicate )
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Uneven Fracture

• Common Type

Anhydrite (CaSO4, Calcium Sulfate )
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Jagged Fracture

• Sharp points in edges that catch on the finger
  when rubbed across

Copper (Cu, Elemental Copper )
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Splintery Fracture

• Fibrous or finely needle shaped minerals and have
  a relatively stronger structure in one direction
  than the other two.

Serpentine (Mg,Fe)3Si2O5(OH)4, Magnesium Iron
Silicate Hydroxide Splintery
Kyanite (Al2 SiO5, Aluminum Silicate Non-fibrous
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Earthy Fracture

• Produces a texture similar to broken children's
  clay

Limonite (A mixture of hydrated iron oxides)
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Identifying Properties Special Properties

• Some minerals can be identified by special
  physical properties.
• Examples
• Magnetism
• Occurs naturally in a few minerals Magnetite
• Fluorescence (glows under ultraviolet light)
• Scheelite
• Reactivity reacts chemically to acids
• Aragonite and calcite
• Optical properties bends light to produce
  double image
• Calcite
• Radioactivity the process that occurs when a
  nucleus decays and emits alpha, beta or gamma
  radiation.

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Special Properties

• Fluorescence minerals that glow in ultraviolet
  light

Scheelite (CaWO4, Calcium Tungstate )
Under ultraviolet
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Special Properties

• Magnetism Acts like a magnet

Magnetite (Fe3O4, Iron Oxide )
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Special Properties

• Electrical

Quartz (SiO2 , Silicon dioxide)
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Special Properties

• Radioactive

Uraninite (UO2 , Uranium Oxide)
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Special Properties

• Reactivity to
• acids

Calcite (CaCO3, Calcium Carbonate )