Important Economic Minerals

Elements:




Iron Oxides:



Gold, Copper, Zinc…
Sulfur
Diamond, Graphite,
Hematite (Fe2O3),
Magnetite (Fe3O4)
Elements and Ores


Usually concentrated by
biological or hydrothermal
processes
Associated with
volcanism (plutonics) or
metamorphism
Rock-Forming
Minerals

Sediments and Sedimentary Rocks

Oxides (e.g., Iron oxides)


Halides (e.g., with Cl- or S-2)


Fe2O3, Fe3O4
NaCl, FeS2
Sulfates (SO4)-2 and Carbonates (CO3)-2
FeSO4, CaSO4, CaSO4,·(2H2O)
 CaCO3, CaMg(CO3)2,

% of Tot. # of atoms
Fe/Mg: Silicon:
Olivine
29%
14%
Systematic Silicate
Mineralogy


Pyroxene
Fig. 2.9
<20%
Group
From bottom to
top



Decreasing
Silica
Increasing
Fe/Mg/Ca
Increasing
Density

Amphibole
Group
<3%
Increasing
Fe/Mg/Ca
Decreasing silica
Mica
<2%
Group
Increasing density
Darker minerals
Quartz
K and Na Feldspar
Ca Feldspar
(0)
(0)
(0)
20%
23%
25%
33%
23%
15%*
Systematic Silicate Mineralogy
and Engineering Properties
Olivine
Mantle
Pyroxene
Group
Increasing
• Melting and • Fe/Mg/Ca Content
crystallizing
• Density
Temperature~
• Susceptibility to
Weathering*
Decreasing
~Quartz
melts first
*All of these
silicates weather to
form Clay Minerals
Except quartz
 Fig. 2.9
Oceanic
#
 Crust
From
bottom
top
to
Amphibole
Group
Increasing
Fe/Mg/Ca
 Decreasing silica
Mica
Group
 Increasing density
 Darker minerals
Cont.

Crust
Quartz
K and Na Feldspar
Ca Feldspar#
Minerals in sediment
Sandy and clayey soils
Rocks (at surface)
Sediment
Weathered to form
Biotite
Quartz
Na Plagioclase
Sediments of:
Quartz
Feldspar
Clay
Calcite
Hematite
Minerals in Rocks
Clastic sedimentary rocks

E.g., Sandstone




Primary minerals: Quartz
and Feldspar
Secondary mineral from
weathering: Clay and
Oxides
Lithified (Compacted
and cemented together)
From Sand
deposited by a
river or beach
Minerals in Rocks
Biochemical and bioclastic sedimentary
Shells, Coral, Calcite and Dolomite in
Limestone



Lithified lime mud
and
Shell fragments
Crystalline or
Bioclastic
Minerals in Rocks
Clastic sedimentary rocks

E.g., Shale


Primary mineral:
Clay
Minor mineral
Quartz and
Feldspar and
Oxides
From mud
deposited in a deep
lake, sea or ocean
Minerals in Rocks
Metamorphic
E.g. Schist
Mica, Quartz and
Feldspars
 Interlocking
crystals
(i.e., crystalline)

Shale metamorphosed
Minerals Changed
in the solid state
by heat and pressure
Minerals in Rocks
Intrusive igneous rocks

E.g., granite


Quartz, Feldspar
and a few
Ferromagnesian
minerals
Tightly interlocking
crystals (crystalline)
Minerals formed
from crystallizing
magma
IV. Igneous Rocks
A. Igneous Rocks and the Rock Cycle
B. Basaltic Volcanism and Volcanic Rocks
(extrusive igneous rocks)
C. Silicic Volcanism and Volcanic Rocks
D. Intrusive Igneous Rocks and
E. Igneous Rock Classification
A. Igneous Rocks
and The Rock Cycle


Geological Materials
Transformation
Processes
Igneous Rock
Solidification

Magma
Partial Melting

Mantle Rock
Fig 3.1
See Kehew, Fig 2.53
% of Tot. # of atoms
Fe/Mg: Silicon:
Olivine
29%
14%
Melting Points of
Silicate Minerals
> 1,100oC


Pyroxene
Fig. 2.9
<20%
Group
From bottom to
top


Increasing
Melting
Temperature
<700oC


Amphibole
Group
<3%
Increasing
Fe/Mg/Ca
Decreasing silica
Mica
<2%
Group
Increasing density
Darker minerals
Quartz
K and Na Feldspar
Ca Feldspar
(0)
(0)
(0)
20%
23%
25%
33%
23%
15%*
Melting of Granite
(Quartz, Na Plagioclase, Biotite)
~600oC
~700o
Quartz Melts
First
~900o
~800o
Na-Feldspar
Begins to melt
~1000o
Silicic
Melt
Biotite begins
to melt
Magma is enriched
in Si, Na, Al (K)
Magma is separated from solid
and melts upward in crust
Partial Melting and Magma
E.g., Silicic mineral melt first
Resulting in Silicic Magma
Fig 3.13
Enriched: O, Si, Al, Na, K,
Depleted: Ca, Fe, Mg
Gasseous: (H2O, CO2)
Magma  Partial Melting
Poor in: O, Si, Al, Na, K, (<50%)
Rich in: Ca, Fe, Mg (>50% wght)
Solidification of Melts
See Kehew, Fig 4.48 Fig 3.12, 3.13
• Magma, Intruded or Extruded,
• Solidifies (crystallizes) to form
• Intrusive or Extrusive
• Igneous Rocks
Igneous Rock
E.g., Granite (Silicic, Intrusive Igneous Rock):
Quartz
Biotite
Na Plagioclase
Crystallized (Solidified)
Silicic Melt
Poor in: Fe, Mg, Ca, (<20%)
Rich in: Silica (>70%)
Formation of Magma

How are rocks melted?




1. Heating ■ 2. Depressurization
3. Increase water content
4. Increased silica content
Where do rocks melt?



Subduction zones (Silicic
and Intermediate magma)
Divergent Plate Boundaries
Mantle Plumes (“Hot Spots”)
Mafic
Magma
Hot and
Low Pressure
Hot and
High Pressure
See Fig. 4.1
Intrusive vs.
Extrusive

Silicic Magmas (& Lavas)




Cool (<700oC)
Viscous
Gaseous (steam of H2O and C02)
Silicic Rocks



Usually intrusive, course-grained,
Silicic (Granite) to Intermediate
(Diorite) rock forms plutons
If extrusive, fine-grained rocks are
formed by explosive volcanoes
Rhyolite or Andesite Volcanoes
Also injects surrounding rocks
with silica laden steam
Batholith made of Plutons
Fig 4.17
Composite Volcano
Dikes: Intruded near a pluton



Silica rich fluids and
rare elements are
injected into cracks
in all directions
Discordant: cutting
across layers
Forming deposits of



Precious minerals
Ores
Precious metals
Extrusive vs.
Intrusive

Mafic Magmas (& Lavas)




Hot (>1000oC)
Non-Viscous (runny, flows easily)
“Dry” (no H2O or C02)
Mafic Rocks



Usually Extrusive, Fine-grained,
Mafic (Basalt) rock forms oceanic
crust, Shield Volcanoes and Basalt
Floods
If Intrusive, course-grained mafic
rocks are formed Gabbro.
If intrusive, Dikes and Sills more
common. (Plutons don’t form)
Fig 3.10
Mafic Sill: Intruded between layers




Mafic magma is less
viscous and hotter so
Does not form plutons
but
Cuts along layers (Sills)
or even
across layers (Dikes)
Also Baked Zones
of adjacent country
rock and Chill Zones
within the intrusion
B. Basaltic Volcanism

1. Types of Rocks are controlled by 
Fig. 3.7


2. Characteristics of volcanism which are contr. by


3. Types of eruptions which are controlled by


4. Type of lava which is contr. by


5. Source of lava which is contr. by


6. Plate tectonics 
Fig. 3.22
1.Types of Rocks
Composition and Texture

Basalt






‘A’a
Pahoehoe
Vesicular Basalt
Pillow Basalt
Columnar Jointing
Obsidian (Glass)
Figs. 4.9, 4.11, 4.17, 4.18
2. Characteristics of Volcanism
Fig. 4.1



Fissures
Shield volcanoes
Cinder cones
Fissures Through Crust
Fig. 3.22
Fig. 4.16
Fig. 4.20
Calderas atop of
Kilauea Shield
Hawaii Cinder Cone
3. Types of Eruptions

Non-explosive

Lava flows,
streams, ponds, floods



Fountains
Spatter cones
Pyroclastic eruptions
4. Types of Lava

Types of lava Basaltic



Hot
Non-viscous
Dry
5 . Source of Lava

Partial melting of mantle



Directly from mantle
Mantle plumes
Divergent plate boundaries
Fig. 3.7
C. Silicic Volcanism

1. Types of Rocks 
Fig. 3.7


2. Characteristics of volcanism


Fig. 3.24
3. Types of eruptions


4. Type of lava


5. Source of lava


6. Plate tectonics 
Fig. 3.24
1.Types of Rocks
Composition and Texture

Andesite (and Rhyolite)


Pumice (quenched glass froth)
Porphyritic Texture (partial
Fig. 4.12
crystallization and extrusion)

Welded Tuffs (welded
pyroclastics)

Breccias (welded, coarse,
angular pyroclatics)
1mm
Fig.
4.10
2. Characteristics of Volcanism

Lava Domes
Composite Volcanoes


Layers of Pyroclastics
(or tephra), ash and
Lava flows
Fig. 4.26
Fig. 4.21
Pyroclastic
Layers
3. Types of Eruptions
Fig. 4.1
Box. 4.19
Mt. St. Helen’s
Cascade Range

Explosive


Pyroclastic Flows and
surges
Lahars (saturated
pyroclastics)
Fig. 4.20
Mt. St. Helen’s Before and After
1 mile
4. Types of Lava

Silicic



Cool
Viscous
Gaseous
5. Source of Lava

Partial melting at
Subduction Zone

Partial melting of
continental crust

Convergent plate
boundaries
Fig. 3.24
Igneous Rock Classification
Intrusive (Plutonic)
Extrusive (Volcanic)
E.g., Basalt
and Gabbro
have two
minerals
 Pyroxene
 Ca-Feldspar
Volume Percent
of Minerals

Kehew Figure 4.58
Lab Manual Fig. 3.8
Continental Crust
Oceanic Mantle
Crust
The
Igneous Rock
Classification
parallels the
systematic
Silicate Mineral
Classification
Framework
Volume Percent
of Minerals
Igneous Rocks
and Silicates
Sheet
Double
Chain
Single
Chain
Iso.
Fig. 2.9
Igneous Rock Classification
Intermediate
Mafic
Granite
Rhyolite
Diorite
Andesite
Gabbro
Basalt
Extrusive
Intrusive
Silicic
Fig. 3.7
(Porphyritic)
Bowen’s Reaction Series
Two series of minerals formed during crystallization of magma
Isolated
Temperature of
Crystallization
Low Silica Magma
1200oC
Gabbro Basalt
1000o
Diorite Andesite
750o
Framework
Sheet
Double
Chain
Single
Chain
Intrus. Extrus.
Kehew, Figure 4.53 (upside down)
Granite Rhyolite
High Silica Magma
Crystallization of Gabbro and Basalt
~1,450oC
~1,400o
~1,350o
Mafic
Melt
Ca-Feldspar
Forms
~1,300o
Olivine
Forms
The remaining
melt is enriched
in silica (Int-Felsic)
If melt is extracted
Ultramafic Rock
Olivine converts will be formed
to Pyroxene
~1,250o
Gabbro
Remaining silica crystallizes into Ca-Feldspar. Intrusive
Cooling: Slowly
Basalt
Extrusive
Quickly
Crystallization of Diorite and Andesite
~1,400oC
~1,300o
~1,200o
Olivine converts
to Pyroxene
Ca Feldspar
absorbs Na
Intermediate
Melt
Ca Feldspar
Forms
~1,100o
If cooled
slowly in the
magma
chamber then
extruded,
Andesite
Porphyry will
be formed
~1,000o
Pyroxene converts Remaining silica
to Amphibole
forms Na-Ca Fldspr.
Diorite
Intrusive
Slowly Cooled
Andesite
Extrusive
Quickly Cooled
Crystallization of Granite and Rhyolite
~1,200oC
~1,100o
~1,000o
Silicic
Melt
Na-Feldspar
forms and grows
~900o
Amph. dissolves
to form Biotite
Pyroxene
forms
Pyroxene dissolves
to form Amphibole
~750o
Remaining silica
forms Quartz
Granite
Intrusive
Slowly Cooled
Rhyolite
Extrusive
Quickly Cooled
Physiographic Map of the World
Reading the features
• Dark Blue (to black) lines are Oceanic Trenches
• Light blue long light blue regions within the darker blue ocean basins are
Mid-Ocean Ridges
• Red linear regions on continents are mountain ranges
Vocanic Hazards








Volcanic Earthquakes
Directed Blast
Tephra
Volcanic Gases
Lava Flows
Pyroclastic Flows and
Surges
Lahars
Debris Avalanches,
Landslides, and Tsunamis
Hawaii Hazards