Earth Science
Earth’s Buried Treasures
An Introduction to Earth
Materials: Minerals
The Importance of Minerals
Definition of a Mineral
A Mineral is:
– Naturally Occurring
– Inorganic
– Solid
– Definite chemical
composition
– Orderly internal
arrangement of atom
Gemstones
Mineraloids lack an internal arrangement of atoms
Rocks vs. Minerals
Minerals are the components of rocks. A thorough understanding of minerals provide a
better understanding of the formation of rocks.
Elements of the Earth’s Crust
An element is a substance that cannot be broken down into simpler, stable substances by
chemical means. Each element has physical and chemical properties that can be used to identify
it. The diagram above shows common elements in Earth’s crust. Approximately 90 elements
occur naturally on Earth. Eight of these make up more than 98%of Earth’s crust.
Major Mineral Group: The Silicates
• Oxygen and Silicon are
the most abundant
elements in the Earth’s
crust so…
• The Silicates are the
most abundant group
• Made up of the SiliconOxygen Tetrahedron
• Identified by the SiO in
the chemical formula
• Example: AlSiO2
Other Mineral Groups
To determine the mineral group, look at the last part of the chemical formula
Other Mineral Groups
Mineral Resources
Earth’s crust contains useful mineral resources. The processes that formed many of
these resources took millions of years. Many of these mineral resources are mined
for human use. Mineral resources can be either metals, such as gold, Au, silver,
Ag, and aluminum, Al, or nonmetals, such as sulfur, S, and quartz, SiO2.
If a volume of rock is
enriched enough in an
element or mineral to
be potential valuable it
is called a mineral
deposit
Mineral Environments of Formation
Mineral Environments refers to the "geologic environments" in which
minerals occur – the types of rocks in which they are found. While some
minerals occur in two or more environments, others tend to be restricted to a
single environment.
–
Chapter18.9
Example: If you think you have found the mineral kyanite in a sedimentary sandstone and see
that it is a mineral formed by metamorphic processes you’ll know it can’t be kyanite. Try
celestite… If you think you have found topaz in a cavity in basalt and read that it is largely
restricted to pegmatite you’ll know it isn’t topaz. And so on.
Mineral Environments of Formation
Ores form in a variety of ways, as shown below. Some ores, such
as ores of chromium, Cr, nickel, Ni, and lead, Pb, form within
cooling magma. As the magma cools, dense metallic minerals sink.
As the minerals sink, layers of these minerals accumulate at the
bottom of the magma chamber to form ore deposits.
By knowing how specific
minerals and the environments
in which they form you can
make an interpretation of
paleo-environments as well as
locate mineral resources. You
can also use this to
differentiate between similar
appearing minerals
Mineral Environments of Formation
The environments of mineral formation and growth are highly varied, ranging from
slow crystallization at the high temperatures and pressures of igneous melts deep
within the Earth's crust to the low temperature precipitation from a saline brine at
the Earth's surface.
Various possible methods of mineral formation include:
- sublimation from volcanic gases
- deposition from aqueous solutions and hydrothermal brines
- crystallization from an igneous magma or lava
- recrystallization due to metamorphic processes and metasomatism
- crystallization during diagenesis of sediments
- formation by oxidation and weathering of rocks exposed to
the atmosphere or within the soil environment.
Mineral Environments of Formation
18.09.c
Igneous
crystallization
Hydrothermal
replacement
Hydrothermal
deposition
Volcanism and
volcanic pipes
Metamorphism
Mineral Environments of Formation
Minerals Formed in Igneous Environments
Quartz
Mica
(Muscovite)
Na/Ca Feldspar
(Plagioclase)
Amphibole
K Feldspar
(Orthoclase)
Pyroxene
Mica
(Biotite)
Olivine
Mineral Environments of Formation
Minerals formed in Metamorphic Environments
Quartz
Serpentine
Na/Ca Feldspar
(Plagioclase)
Chlorite
K Feldspar
(Orthoclase)
Mica
(Biotite)
Garnet
Mica
(Muscovite)
Calcite
Mineral Environments
of Formation
Important Base
Metal Deposits
Ores
Hematite (Iron)
Bornite (Copper)
Galena (Lead)
Sphalerite (Zinc)
Bauxite (Aluminum)
Apatite
(Phosphorous Used in Fertilizers)
Mineral Environments of Formation
Where do Platinum deposits occur?
Most Platinum deposits are associated with mafic or ultramafic igneou rocks that come from the
mantle and rose into the crust.
Pictured is the Bushveld Complex in South Africa. The dark layers are platinum and chromite and the light layers are anorthosite.
Mineral
of Formation
TwoEnvironments
Other Types
of Metal Deposits
Mississippi
Valley
lead-zinc
deposits
Sudbury
nickel
deposits
18.11.d
Shatter cones
(from impact)
How do
precious of
metal
deposits form?
Mineral
Environments
Formation
Veins from hot water Veins in
metamorphic rocks
Gold in gravel
Gold-bearing
conglomerates (placer
By-product gold
deposits)
Low-grade
gold deposits
18.10.a
Mineral Environments of Formation
Quartz Vein with Gold
Deposits
Diamond Formation
Mineral Environments of Formation
Kimberlite is the type of
rock typically associated
diamonds
Diamonds do not originate from the
metamorphism of coal but rather form in the
mantle and are brought to the surface by
geologic features called kimberlite pipes
Mineral Environments of Formation
Other sources of diamond formation:
1) Kimberlite Pipe (most common)
2) Subduction Zones
3) Asteroid Impact Sites
4) Meteorites (brought by meteorites)
Mineral Environments of Formation
Rubies are a form of corundum, a rare mineral made up of densely
packed aluminum and oxygen atoms, which are normally colorless.
When other atoms are substituted for a few of the aluminum ones,
bright hues emerge. Small amounts of chromium impart the deep
red color of ruby, traces of titanium and iron produce the stunning
blue of sapphire, and chromium and ferric iron create the delicate
orange shades of the extremely rare and costly padparadscha.
Mineral
Environments
Formation
Where
do Copper of
Deposits
form?
Porphyry copper
deposits
Massive sulfide
deposits
Sedimentary copper
deposits
18.11.a
Mineral Environments of Formation
18.09.c
Formation by weathering
Weathering enrichment
Mechanical concentration
Low-temperature precipitation
Mineral Environments
of Formation
Important
Minerals
Minerals formed From Weathering
Quartz
Hematite
Kaolinite
Bauxite
Mineral Environments of Formation
Gold that has been liberated by weathering and erosion get carried away
by streams and deposit within placer deposits
Minerals as Indicators of Ancient Environments
Where do base metal deposits form?
Most of our iron ores are mined from
formations called banded iron formations
(BIF’s) . These iron and quartz rich layers
are an indication of the Great Oxygenating
event that occurred during the Precambrian
2 billion years ago
Other iron ore deposits form as
magma intrudes into the crust and
releases metal rich fluids
Mineral Environments of Formation
Evaporites and Precipitants
Gypsum and Halite are examples of
evaporites. These minerals from in low
temperature aqueous environments.
Calcite and Travertine are examples
of precipitants. These minerals
precipitate out of water under the
correct environmental conditions.
Marine evaporite deposits in the United States
Minerals as Indicators of Ancient Environments
Gypsum and Halite are evaporites that form by the evaporation of ocean water. Thus
these deposits indicate the location of ancient seas
Minerals as Indicators of Ancient Environments
This image, taken by the Mars Exploration
Rover Opportunity's panoramic camera, is
an approximate true-color rendering of the
"Berry Bowl," a rock in the "Eagle Crater"
outcrop that contains pebble-like hematite
spherules
Marble-like hematite concretions litter
the Navajo Sandstone surface in
southern Utah's Grand StaircaseEscalante National Monument.
Minerals as Indicators of Ancient Environments
Conclusion
Earth’s Buried Treasures
An Introduction to Earth
Materials: Minerals