Lecture 5: Mineral Properties

Atom

Composed of an electron made up of negatively charged electrons and a nucleus

  • Nucleus has about the same number of positive protons and neutral electrons
  • Outer shell has about the same number of negative electrons


Element

A grouping of the same atoms that all have the same number of protons

  • Example: carbon, oxygen, uranium
  • Isotope - elements with the same atomic number but different number of neutrons


What is a Mineral?

Mineral - A material composed of a single or multiple elements held together by chemical bonds

  • Covalent ionic bonds are strong
  • Metallic bonds are weaker
  • Van der Waals bonds are the weakest


Fundamental Properties of Minerals

  • Naturally occurring - produced in nature

Solid - can maintain its shape

Inorganic - sugar and protein are not minerals

  • Crystalline structure (orderly internal arrangement) - structure is fixed
  • Definable chemical composition - possible to write a chemical formula for it


Is Ice a Mineral?

  • Naturally occurring: Yes
  • Solid: Yes when it is cold out
  • Crystalline structure (orderly internal arrangement): Yes
  • Definable chemical composition: Yes (H2O)
  • Inorganic: Yes

Mineral Properties

  • Color
  • Streak - Rubbing the material against a porcelain plate
  • Luster - the way a mineral surface scatters light, can be metallic or non-metallic
  • Hardness - ability to resist scratching, Mohs scale
  • Specific Gravity
  • Crystal Habit - shape/ structure of a mineral
  • Cleavage - how a mineral breaks
  • Other - reacts with acid, magnetic, salty, etc


Mohs Hardness Scale

  • Measure of the relative ability of a mineral to resist scratching

P190-01

Cleavage vs. Crystal Habit

Crystal form - shape of a crystal. Crystal face is a single surface

Cleavage - tendency of the crystal to split along definite structural planes

  • Forms in directions where bonds holding atoms together in the crystal are the weakest
  • Cleavage planes can be repeated


Ionic Bond

  • Atoms EXCHANGE but DO NOT SHARE electrons
  • Atoms are then attracted to each other because of their charge
  • Example: Halite; mystery mineral #1
  • 3-sided crystal form right angles, 3 directions of weakness, can be easily dissolved


Covalent Bond

  • Atoms SHARE electrons to make themselves more stable
  • Example - Diamond
  • Carbon atoms are arranged in a tetrahedral, all bonds are strong (covalent)
  • Example - Graphite
  • Carbon atoms arranged in hexagonal sheets, sheets are connected by weak bonds (van der Waals)


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