Minerals

NOTE CHANGE: Study questions will be posted on web page on Fridays (ie. before your quizzes).
 Use the questions to help you study. Don’t memorize!

Importance:
• The building blocks of rocks
• resources, gemstones  (link for where to find gemstones, link for gemstone pictures)
Geologic definition

• naturally occurring
• inorganic
• crystalline solid
• narrowly defined chemical composition
• characteristic physical properties
 Diamond and graphite have same composition -- carbon (C)
But, very different properties

Why? Different chemical bonds

Elements and Atoms
• element: cannot be broken by chemical means.
• Atom: smallest particle with all the properties of a given element.
Nucleus:
Proton: + charge
Neutron: no charge

Electron: - charge, orbiting

Bonding: Tendency of an element to bond relates to number of electrons.
• some non-reactive
• some give or receive electrons:

– become + or - charged ions
– attractive force between + and - charged ions forms ionic bonds
• some share electrons between two atoms, forming covalent bonds
• metallic bonds result from sharing electrons between many atoms
• Van der Waals bonds: very weak electrical attraction

Bonds give minerals an ordered structure (minerals are crystalline)

Crystallization (the forming of bonds) can occur by:
• change in temperature or pressure (ie., ice from water)
• precipitation from a solution (example salt forming as water evaporates)

 External crystal form not always present.
 

Chemical Composition

Mineral composition shown by chemical formula. Example: Corundum: AlO2

Variation is possible. Other ions can sub for Al3+ in trace amounts - Ionic substitution:
    Chromium: ruby
    Iron/Titanium: sapphire

Mineral Groups

More than 3500 minerals identified.
Only ~two dozen are common. Why?
• 8 elements make up bulk of earth’s crust.
• Oxygen and silicon: 74%

#1: oxygen  #5 calcium
#2: silicon  #6 sodium
#3: aluminum #7 potassium
#4: iron   #8 magnesium

 Silicate minerals

Basic building block of all silicate minerals is the silica tetrahedron.
• Bonds with ions of other elements or other silica tetrahedra

Isolated with other ions (olivine)

Chains: other ions between chains (pyroxene, amphiboles)

Sheet: with other ions between sheets (clay minerals, micas)

Framework: 3-D network (feldspar, quartz)

  Why structure is important: clay minerals
Clay minerals are sheet silicates. Some clay minerals are weakly bound between the silicate sheets, and allow space for water to fill, causing expansion.

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Curious about minerals? Other web pages have been linked by the textbook publisher.