Transcript Compared to the desolate surface of the Moon, Earth must have

Minerals
I. Minerals
Definitions – Earth Materials
A. Rock: naturally occurring aggregate of
one or more minerals
B. Mineral: naturally occurring solid with a
definite chemical composition and an
orderly internal structure.
Natural: synthetic gems and other
substances created by chemists are
not minerals
Solid
Definite chemical composition: consists
of one or more chemical elements in
specific proportions
Orderly internal structure: elements are
arranged in a systematic way that is
the same in every sample of that
particular mineral
Rocks and Minerals
At one time or another, you
have probably held a rock
in your hand
Recall the color.
Recall the size.
The word rock refers to
solid mineral deposits.
Rocks are minerals, but not all
minerals are rocks. Minerals are
all substances that can't be
classified as "animal" or
"vegetable."
Minerals
Metals ores found in the
earth, like gold and silver,
are minerals.
Crystalline substances, like
salt and quartz, are
minerals.
Homogeneous natural
substances, like water and
gas, are also minerals.
These non-solid minerals?"
Rock: an aggregate of one
or more minerals
Minerals
(a) atomic structure and
chemical reactions: a review
(b) What is a mineral?
(c) Classification of minerals
(d) Silicate minerals
What is a mineral?
First we need to
understand atomic
structure of elements.
Atomic structure and
chemical reactions
STRUCTURE OF
ATOMS: Atom is the
smallest unit of an
element that retains the
physical and chemical
properties of that
element.
Atom: the smallest particles of an
element that retain all of the
element’s chemical properties
Chemical Compounds: specific
combinations of one or more
elements.
Atoms bond together to form
compounds
a. SiO2, NaCl, PbS, Fe2SiO4,
CaAl2Si2O8
All of the above are chemical
formulas of minerals
b. Minerals are essentially
chemical compounds;
elements, in certain
proportions, bonded together
A. Relative abundances of
elements
Composition of Earth
Crust
Entire Earth
1. Oxygen (O) 45.2%
29.3% (2)
2. Silicon (Si)
27.2%
14.7% (3)
3. Aluminum (Al) 8.0
1.2% (8)
4. Iron (Fe)
5.8%
34.8% (1)
5. Calcium (Ca)
5.1%
1.4% (7)
6. Magnesium (Mg) 2.8%
11.3% (4)
7. Sodium (Na)
2.3%
8. Potassium (K)
1.7%
Sulfur (S)
3.3% (5)
Nickel (Ni)
2.4% (6)
Total
98.1%
98.4%
Of the 92 naturally occurring
elements, 8 make up >98% of
the Earth’s continental crust
Most minerals in the crust are O
and Si based rocks (silicates)
Most minerals in the mantle are
O-Si-Fe-Mg based rocks
CHEMICAL REACTIONS
and TYPES OF CHEMICAL
BONDS
Ions = atoms that gained and
lost electrons:
Ions -- after gain or loss of an
electron, atoms are no longer
electrically neutral.
When Na loses an electron it
becomes a Na ion.
Positive ions = cations,
Negative ions = anions.
CHEMICAL REACTIONS
TYPES OF CHEMICAL
BONDS
Relative sizes and charges of these
elements’ atoms and ions
1. Given two elements of equal
abundance, the element that will
contribute more readily in a mineral
is the one that “fits” better with
the other elements.
2. Ions pack together as closely as
possible (large negative ions with
small positive ions in the “holes”.
3. If amount of one element runs low,
it may be replaced by another.
TYPES OF
CHEMICAL BONDS
One type of atomic bond
is:
Ionic substitution: ions
of similar size and shape
(charge) replace one
another within a crystal
structure
Na (+1) and Cl (-1), + and – attract, so Na
loses an electron and Cl gains an electron
For example Mg and Fe2+
in olivine: (Fe, Mg)2SiO4 )
Ionic substitution
Ions of similar size and
shape (charge) replace one
another within a crystal
structure
Ca and Mg can substitute
each other
O and Ca can not replace
another
The temperature and
pressure at the time of
formation (Structural
Variation)
Polymorphs: minerals with the
same composition, but different
structures because they formed
under different conditions of heat
and pressure
For example, diamond and
graphite are both pure carbon,
one very hard & one soft.
Diamond needs high pressure
(>90 miles)
Graphite more stable at Earth’s
surface
III. Identifying Minerals
Identifying minerals is the key to geology.
We ID the minerals to know what rock it is
and where it came from.
The minerals tell us a story about where the
rock formed and under what conditions
A.
Color: first thing you notice, but least
reliable, can vary greatly (quartz, calcite,
salt)
Color depends on the composition and
structure.
Corundum = clear
Chromium = red rubies
Titanium & Iron = blue sapphires
Lithium = pink
Copper = green
III. Identifying Minerals
B. Luster; how its surface reflects light- its shininess
Metallic
Silky
Vitreous (glassy)
Earthy (dull)
C. Streak—the color of a mineral in its
powered form.
Scrape the mineral across an unglazed
porcelain tile (streak plate)
Different color powder than how the
mineral looks alone
III. Identifying Minerals
D. Hardness: how hard it is - resistance to
scratching or abrasion
Scale from 1-10
Diamond
Steel
6.5
Glass
5-6
Copper penny
Fingernail
Graphite
10
3.5
2.5
1-2
E. Smell and Taste
Sulfur- rotten eggs
Halite- salty
Sylvite- bitter
F. Effervescence
Rocks containing CO3 react with HCl to
form CO2 gas
III. Identifying Minerals
F. How they break
1.
Cleavage: tendency to break
consistently along distinct planes in
the crystal structure due to weak
bonds---break along flat surfaces
called cleavage planes
1. cubic—halite
2. sheets—micas
3. rhombus—calcite
2. Fracture—breaks are jagged and
irregular
conchoidal fracture: breaks like glass curved, shell shaped surface
Int-A.02b
Dr. Kent Ratajeski, Department of Geology
and Geophysics, University of Wisconsin,
Madison
Analytical techniques
X-Ray Diffraction
Nobel Prize for
determining the structure
of halite (salt)
Microprobe
Ion Probe