Minerals, Plummer Chapter 2

1
March 1, 2004
Exams- so far so good! Exams will be returned
and discussed after all make-ups are completed.
Minerals, Plummer Chapter 2

• What is a mineral?

• Silicate minerals

• Gemstones

• Test your diamond-buying skills

2
What is a mineral? The traditional definition

• Naturally occurring substance

• Solid

• Inorganic

NOTE many minerals are produced by BOTH
inorganic AND biological processes
(biomineralization). Calcite - shells of marine
organisms Magnetite- bacteria Apatite- bones and
teeth

• Has a set of physical properties that are the
  same for any and
• all samples of a given mineral.

3
Mineral or Not a Mineral
Halite, NaCl ?
4
Mineral or Not a Mineral
Ice, H2O ?
Liquid H2O ?
5
Mineral or Not a Mineral
Amber (C10H16O) ?
6
Mineral or Not a Mineral
Pearls?
7
Crystal Structure is usually the sticking point
for mineral/not a mineral
Crystallinity- a regularly repeating pattern
Linear pattern (1-dimensional)
8
What do I get if I put several chains side by
side on the floor?
2 dimensional pattern Map View
What do I get if I stack this 2-D pattern one on
top of the other from the floor up to the ceiling?
9
3-dimensional pattern
Connect the centers of the blue circles- cubic
structure
Plummer et al., Physical Geology 9th edition,
McGraw Hill Inc, Fig 2.02
10
NaCl - table salt
Sodium (Na)
Chlorine (Cl)
Plummer et al., Physical Geology 9th edition,
McGraw Hill Inc, Fig 2.02
NaCl held together by ionic bond, which is easy
to break --gt cleavage and hardness
11
The building blocks of minerals
A (paraphrased) question from Super Millionaire
What is the most abundant element in the Earths
crust?
Element
symbol
Oxygen
O
Silicon
Si
Aluminum
Al
8 elements make up 98.6 of the Earths crust.
Iron
Fe
Calcium
Ca
Sodium
Na
Potassium
K
Magnesium
Mg
12
Main rock-forming mineral groups
Silicates

• make up the majority of crustal rocks

• building block is SiO4 tetrahedron

Oxides

• composed on metal oxygen

Carbonates

• important component of sedimentary rocks

• building block is CO3 ion

13
SiO44- complex ion

• A group of ions that is so tightly bound
  together
• that they act like a single unit.

• Building block of silicate minerals

• 1 silicon ion 4 oxygen ions
• arranged in a triangular pyramid

• Electrical charge of -4

14
Plummer et al., Physical Geology 9th edition,
McGraw Hill Inc, Fig 2.07
15
Silicate tetrahedron SiO44-
16
Tetrahedron Viewing
View from the top, looking down. Top point
of tetrahedron facing you
Flat base of tetrahedron facing you. Top point of
tetrahedron pointing away from you.
17
Nesosilicates (island silicates)
SiO44- tetrahedron forms ionic bonds with cations
such as Mg2, Fe2
Example Olivine
Mg2SiO4 - Fosterite
Fe2SiO4 - Fayalite
(Mg, Fe)SiO4 Solid solution
18
Olivine nesosilicate structure (island silicate)
Why Mg OR Fe?

• Same size

• Same electrical
• charge

19
Corner Sharing Base to Base
side view
3-D Side View
20
Inosilicicates Single Chains (Pyroxene)
SiO3 Chain forms ionic bonds with cations above
the tip and below the base
2 Si 6 O
Plummer et al., Physical Geology 9th edition,
McGraw Hill Inc, Fig 2.11
21
Extra slide. Not shown in class. Not for exams.
For your interest.
Corner Sharing Tip to Tip
Face sharing
22
Extra slide. Not shown in class. Not for exams.
For your interest.
Assembling a Single Chain Silicate (Pyroxene)
23
Extra slide. Not shown in class. Not for exams.
For your interest.
Pyroxene- Wheres the cleavage?
90 cleavage
24
Extra slide. Not shown in class. Not for exams.
For your interest.
This wont work. No gold, silver, or
uranium found with pyroxens.
25
Double Chain Silicates (Amphibole)
PAIR of SiO4 chains that link by corner sharing
in 2 directions
Plummer et al., Physical Geology 9th edition,
McGraw Hill Inc, Fig 2.11
26
Extra slide. Not shown in class. Not for exams.
For your interest.
Amphibole formula is long lots of space for
small and medium cations
Cations include Na, K, Ca2, Mn2, Fe2, Mg2,
Fe3, Al3, Ti4
Plummer et al., Physical Geology 9th edition,
McGraw Hill Inc, Fig 2.11
27
Extra slide. Not shown in class. Not for exams.
For your interest.
60-120 Cleavage in Double Chain Silicates
(Amphibole)- (actually 56 - 124)
breaking at the molecular scale
What human eyes see at the macro scale
28
What is Jade?
Both pryoxene AND amphibole are Jade.
Jadeite NaAlSi2O6 Nephrite Ca2(Mg,Fe)5Si8O22(O
H)2
Other Jades African jade Green garnet Amazon
jade Green K-feldspar Indian jade Green quartz
29
Asbestos- generic name for fibrous amphibole
Plummer et al., Physical Geology 9th edition,
McGraw Hill Inc, Box 02.03.f1, photo by C.C.
Plummer
30
Ring Silicates- Beryl
Stack of SiO4 rings, built up out of the plane of
screen
31
(No Transcript)
32
Muscovite
Plummer et al., Physical Geology 9th edition,
McGraw Hill Inc, Fig. 2.14
33
Clay minerals talc, kaolinite, illite, chlorite,
montmorillonite
You know them better as baby powder,
kaopectate/non-dairy creamer, facial mask,
soapstone, and kitty litter.
Main difference- ions that make up the middle of
the sandwich
34
(No Transcript)
35
Quartz

• All oxygens are shared

• No cleavage. Covalent bonds
• are equally strong in all directions

• Hardness of 7 on Mohs scale,
• also due to crystal structure.

• very roomy structure.
• Can accommodate large cations.
• Gold, silver always found with quartz

36
What makes a mineral a gem?
Gemstones- beautiful, rare, durable
Fluorite- gem or not a gem?
37
Birthstones- Gem names
Garnet
Amethyst
Turquoise
Topaz
Aquamarine
Diamond
Opal
Sapphire
Emerald
Peridot
Pearl
Ruby
38
Birthstones- The real names!
Garnet
Quartz
Hydrous copper phosphate
Al-F silicate
Beryl
Amorphous quartz
Diamond
Corrundum
Beryl
Olivine
Pearl
Corrundum
39
Ruby and Sapphire- forms of Corundum Al2O3
Ruby- corundum with chromium Sapphire- corundum
with iron and titanium
40
A quick guide to buying diamonds-

• Color
• Cut
• Clarity
• Carat

41
Gem- rare, beautiful, durable
A typical diamond deposit yields 5 grams of
diamond per 1000 kg of rock mined.
42
1. Color- Which one is the most valuable?
Colorless
Near colorless
Faint yellow
Very Light yellow
Light yellow
Fancy yellow
43
The Hope Diamond
45 carats
Possibly the re-cut (4 times) Tavernier Blue
Diamond, which was reported at 112 carats in the
year 1668.
44
2. Cut
Table
Crown
Main pavillion
45
Cutting Diamonds
Marshak, S. Earth, Portrait of a Planet, W.W.
Norton, Fig. 5.26
46
Why are diamonds cut this way?
Facets control the pat of light traveling through
the diamond. The more light that exits the top
(crown), the more it sparkles.
Pat of light in a round brilliant diamond
47
Imperfections in the cut
48
3. Clarity
Are there blemishes on the surface, or inclusions
inside the diamond?
49
4. Carat weight
1 carat (ct.) 200 milligrams
Big diamonds are more rare than little
diamonds. A 2 ct diamond costs more than 2 times
a 1 ct. diamond.
Note carat weight NOT THE SAME as gold karats.
Gold is made of 24 parts. Karats indicates how
many of those 24 parts are gold. 14 karat gold
14 parts gold 10 parts alloying metal (copper,
nickel, silver) 18 karat gold 18 parts gold 6
parts alloying metal.
50
Is my diamond a fake?!
Zirconium Oxide (ZrO2) Cubic Zirconia
Silicon Carbide (SiC) Moissanite
Extra credit for exam 2 How can you tell the
difference between a real diamond and one of
these substitutes Using physical
properties? Note- you will not be allowed to
leave the room during exam 2 to consult an
appraiser.