Download Elements and Minerals

GEOL 0820
Ramsey
Natural Disasters
Spring, 2017
LECTURE #3: Elements & Minerals
Date: 12 January 2017
I. Recitations start next week!
• please make sure you attend the class and talk with your TA about what is
expected
II. Today: From the “big picture” to the VERY small one!
• from large-scale hazards to the scale of atoms
• critical for understanding the building blocks of geology
• we will not spend as much time on this subject as other introductory geology
classes
o you will get a good review in the recitation
o next class we’ll examine how minerals combine into common rock types
III. What is a mineral?
• definition: a naturally occurring, inorganic solid with a specific chemical
composition and a specific regular arrangement of atoms
o very precise definition and they have specific physical and chemical properties
•
identifying minerals and rocks takes practice and experience
o one of the harder skills to acquire
o other courses in the Department of Geology devote more time and energy to
the details
 for example, there are five labs devoted to rocks and minerals in the
Physical Geology Lab (GEOL 0055) class
•
mineral is made up of atoms
o atom: smallest particle of an element that still retains the properties of that
element
 made up of protons, neutrons and electrons
 protons (+) & neutrons (o) form the nucleus
 electrons (-) orbit the nucleus
•
•
element: substance that cannot be broken down into other substances
can a mineral be an element??
•
atomic number
o the number of protons in an atom
o example: hydrogen (H) has 1 proton
o example: oxygen (O) has 8 proton
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•
periodic table: arrangement of all elements by their atomic number
•
isotope: an element with varying amount of neutrons
o example: most (98.9%) carbon atoms have 6 neutrons (12C)
o example: radioactive variety has 8 neutrons (14C)
Element
Oxygen
Silicon
Aluminum
Hydrogen
Sodium
Calcium
Iron
Magnesium
Potassium
Titanium
Weight %
46.60
27.72
8.13
0.14
2.83
3.63
5.00
2.09
2.59
0.44
Atomic Wt.
16
28
27
1
23
40
55.8
24.3
39
49
•
oxygen dominates the Earth's crust
o 3 times as abundant as Si
o Si is much more abundant than the other elements!
o minerals naturally grow from whatever elements are available
 therefore, a lot of minerals contain O and Si
 of the several thousand different minerals on earth about 95% contain O
and Si
 these are called the silicate minerals
 most common silicate: quartz
•
Silica Tetrahedra (SiO4)
o “building block” of most rocks and minerals
o defines the crystal shape, properties, and appearance of the different silicate
minerals
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o can have different long range order of the tetrahedra in combination with each
other or other atoms
 single (isolated): “olivine” (no shared oxygen atoms)
 chain structure: “pyroxene” (2 shared oxygen atoms)
 double chain structure: “asbestos” (2 shared oxygen atoms)
 sheet structure: “mica” (3 shared oxygen atoms)
 framework structure: “quartz” (all 4 shared oxygen atoms)
IV. Atomic structure of minerals
• all minerals are built from regular, repeating arrangements of atoms
• this regular structure that makes a crystal a crystal
o a piece of wood is a solid, but it has no regular arrangement of atoms; it is not
a crystalline solid
o glass, bricks, plastic, etc. are also not crystalline solids
silica tetrahedra (SiO4)
•
sodium chloride structure (NaCl)
mineral categories
Native elements
gold (Au), copper (Cu), diamond
(C), sulfur (S)
Oxides/Hydroxides Fe2O3, Al2O3, H2O (ice)
Halides
NaCl, KCl, CaF2
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Sulfides
PbS, ZnS, FeS2
Sulfates
CaSO4, BaSO4
Carbonates
CaCO3, FeCO3, (Ca,Mg)(CO3)2
Phosphates
Ca5(PO4)3(OH,Cl,F)
o other mineral indicators (will go over these in recitation in more detail):
 color
 crystal habits
 density
 luster
 cleavage
 streak
 transparency
 fracture
 crystal system
 hardness
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