Earth’s Buried Treasures An Introduction to Earth Materials: Minerals Earth Science

Earth’s Buried Treasures

An Introduction to Earth Materials: Minerals

Earth Science

The Importance of Minerals

Definition of a Mineral

A Mineral is: – Naturally Occurring– Inorganic – Solid– Definite chemical

composition– Orderly internal

arrangement of atom

Mineraloids lack an internal arrangement of atoms

Gemstones

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 Silicon-Oxygen 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

If a volume of rock is enriched enough in an element or mineral to be potential valuable it is called a mineral deposit

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.

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.

– 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.

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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

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.

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.


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Igneous crystallization

Hydrothermal deposition

Hydrothermal replacement Metamorphism

Volcanism and volcanic pipes


Minerals Formed in Igneous Environments

Quartz Na/Ca Feldspar K Feldspar Mica (Plagioclase) (Orthoclase) (Biotite)

Mica Amphibole Pyroxene Olivine

(Muscovite)


Minerals formed in Metamorphic Environments

Quartz Na/Ca Feldspar K Feldspar Mica Mica (Plagioclase) (Orthoclase) (Biotite) (Muscovite)

Serpentine Chlorite Garnet Calcite


Important Base Metal Deposits

Ores

Hematite (Iron) Galena (Lead) Bauxite (Aluminum)

Bornite (Copper) Sphalerite (Zinc) Apatite (Phosphorous Used in Fertilizers)


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.


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Mississippi Valley lead-zinc deposits

Sudbury nickel deposits

Two Other Types of Metal Deposits

Shatter cones (from impact)


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Veins from hot water Veins in metamorphic rocks

Gold in gravel

Gold-bearing conglomerates (placer deposits)

Low-grade gold deposits

By-product gold

How do precious metal deposits form?Mineral Environments of Formation

Quartz Vein with Gold Deposits


Diamond Formation

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

Kimberlite is the type of rock typically associated diamonds



Other sources of diamond formation:1) Kimberlite Pipe (most common)2) Subduction Zones3) Asteroid Impact Sites 4) Meteorites (brought by meteorites)

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.


18.11.a

Porphyry copper deposits

Massive sulfide deposits

Sedimentary copper deposits

Where do Copper Deposits form?Mineral Environments of Formation

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Weathering enrichmentFormation by weathering

Mechanical concentration Low-temperature precipitation


Important Minerals

Minerals formed From Weathering

Quartz Kaolinite

Hematite Bauxite


Gold that has been liberated by weathering and erosion get carried away by streams and deposit within placer deposits


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

Minerals as Indicators of Ancient Environments

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 StatesMinerals 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

Marble-like hematite concretions litter the Navajo Sandstone surface in southern Utah's Grand Staircase-Escalante National Monument.

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


http://www.astrobio.net/news/article1022.html

http://antwrp.gsfc.nasa.gov/apod/ap040405.html


Earth’s Buried Treasures

An Introduction to Earth Materials: Minerals

Conclusion

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Earth’s Buried Treasures An Introduction to Earth Materials: Minerals Earth Science