Transcript Sixth lecture - 16 September, 2013

Geology in the news today:
Flooding continues in
Colorado, with 5
confirmed dead and over
1,000 people still not
located.
The area under water is
now equivalent in size to
the state of Delaware.
This is the
roadway in front
of the home of
Lindsay Masters
'06.
See http://tinyurl.com/n7ekbwd for a National Geographic story on the linkage between
these floods and global climate change.
Chemistry of the Earth
and an
Introduction to Minerals I
Only EIGHT elements make up >98% of
the entire Earth:
Iron (Fe)
34.8%
Oxygen (O)
29.3%
Silicon (Si)
14.7%
Magnesium (Mg)
11.3%
Sulfur (S)
3.3%
Nickel (Ni)
2.4%
Calcium (Ca)
1.4%
Aluminum
(Al)most abundant
1.2%
NOTE
that Fe is the
in the
Earth as a whole!
CONTINENTAL CRUST is enriched in lighter elements
Oxygen
Silicon
Aluminum
Iron
Calcium
Magnesium
Sodium
Potassium
O
Si
Al
Fe
Ca
Mg
Na
K
45.2% of crust
27.2%
8.0%
5.8%
5.1%
2.8%
2.3%
1.7%
O + Si = ~72% of the crust; SILICATE minerals are
far and away the dominant group on Earth.
Quartz (SiO2) is one of the most common minerals
(see text, pp. 53 & 54)
ELEMENTS COMBINE via chemical bonding
a) IONIC BONDING occurs when an element gains or loses
an electron to have a complete outer shell; this occurs when
elements have many or very few electrons in outer shell.
(e.g., K, Na, Cl)
Size of elements is also a factor
in mineral formation.
Positive ions (cations) are
usually smaller than negative
ions (anions).
Smaller positive ions tend to fit
in spaces between larger
negative ions.
Structure of halite - NaCl showing ionic bonding at work
b) COVALENT BONDING occurs when elements have
moderate numbers of electrons (e.g., Si, C, Fe+++), so it's
easier for them to share electrons than to strip or fill an
outer shell per each atom.
Structure of ethane, a gas,
showing covalent C-C and C-H
bonding
Water is also held together
by covalent bonds
Covalent bonding forms the
strongest bonds holding
minerals together.
ALSO critically important is IONIC
SUBSTITUTION (the substitution of one ion
for another of similar size and the same or a
close electrical charge)
TWO are extremely common and VERY important :
1.
This can be illustrated in the structure of the rock-forming
mineral OLIVINE:
2.
THIS pair of ions is critical - because both silicon and
aluminum are so abundant. This characterizes THE
major mineral group that makes up over half the
entire crust - the feldspars!
HOWEVER, this also sets up a charge imbalance!
This is normally accommodated by addition
of K+, Na+ and/or Ca++ to the minerals.
Soooo, what IS a mineral, anyway?
1. Naturally occurring
2. Inorganic solid
3. Has a constant chemical composition, or
one varying within defined, set limits
4. Has a crystalline (ordered) internal
structure. ( This is reflected in the crystal form! )
QUESTION: Is the January ice on
Johnson Pond a mineral ???
Is wood a mineral ?
Is glass a mineral ?
Critical to remember is that ALL minerals
are stable ONLY under specific
temperature-pressure conditions!
Minerals that have both silicon and
oxygen in them are the silicate minerals.
These comprise 95% of the crust – these
are the principal rock-forming minerals.
The NON-silicate minerals (i.e., all the
others) are, save the carbonates, most
important for their economic significance.
1. The first group is the simplest group: Native elements . These
are comprised of a single element, not in combination with
anything else.
Gold
Diamonds
Graphite
Native
copper
Native silver
Native sulfur
2. Second group is the Sulfides. Many are major ores. These are
comprised of a metal plus sulfur.
Chalcopyrite -> Cu
Bornite -> Cu
Pyrite – FeS2 – an important
rock-forming mineral
Sphalerite -> Zn ….
Galena -> Pb
Molybdenite -> Mo
Sulfide minerals, and Native Sulfur (from coal seams)
give rise to
,
an environmental disaster if left
untreated. Though some of this
acidic drainage occurred naturally
before mining began, access to the
minerals responsible was greatly
enhanced by mining activities.
3. Third group is the Oxides and Hydroxides. Many of these
are also major ores. These are comprised of a metal plus
either oxygen or an (OH) group, or both.
Magnetite
Hematite
Limonite
The three major ores of iron , mined worldwide
Bauxite is a blend of AlOOH, Al (OH)3, and other
aluminum oxides and hydroxides ----->
A. Is Bauxite a mineral?
B. Why is this specimen red?
C. What would IT be good for?
Other important oxides include:
Corundum - Al2O3
Used to be
mined
extensively for
abrasives now most
important for
the colored
varieties …..
And the
Oriental
emerald 
All coloration is due to trace impurities ...
Rubies ….
 sapphires
4. The fourth group is the Halides - made up of a metal plus
a halogen - usually Fluorine or Chlorine
Halite - NaCl
Halite and Sylvite
show well the
influence of
internal structure
on the ultimate
shape of the
mineral grains.
Sylvite - KCl
Fluorite - CaF2 - is also a very important halide mineral
As you can guess
from these
pictures, fluorite
can be practically
ANY color!
WHY???