Earth’s Buried Treasures An Introduction to Earth Materials: Minerals Earth Science.
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Transcript of Earth’s Buried Treasures An Introduction to Earth Materials: Minerals Earth Science.
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
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.
Chapter18.9
Mineral Environments of Formation
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.
Mineral Environments of Formation
18.09.c
Igneous crystallization
Hydrothermal deposition
Hydrothermal replacement Metamorphism
Volcanism and volcanic pipes
Mineral Environments of Formation
Minerals Formed in Igneous Environments
Quartz Na/Ca Feldspar K Feldspar Mica (Plagioclase) (Orthoclase) (Biotite)
Mica Amphibole Pyroxene Olivine
(Muscovite)
Mineral Environments of Formation
Minerals formed in Metamorphic Environments
Quartz Na/Ca Feldspar K Feldspar Mica Mica (Plagioclase) (Orthoclase) (Biotite) (Muscovite)
Serpentine Chlorite Garnet Calcite
Mineral Environments of Formation
Important Base Metal Deposits
Ores
Hematite (Iron) Galena (Lead) Bauxite (Aluminum)
Bornite (Copper) Sphalerite (Zinc) 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 Environments of Formation
18.11.d
Mississippi Valley lead-zinc deposits
Sudbury nickel deposits
Two Other Types of Metal Deposits
Shatter cones (from impact)
Mineral Environments of Formation
18.10.a
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
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
Mineral Environments of Formation
Mineral Environments of Formation
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.
Mineral Environments of Formation
18.11.a
Porphyry copper deposits
Massive sulfide deposits
Sedimentary copper deposits
Where do Copper Deposits form?Mineral Environments of Formation
18.09.c
Weathering enrichmentFormation by weathering
Mechanical concentration Low-temperature precipitation
Mineral Environments of Formation
Important Minerals
Minerals formed From Weathering
Quartz Kaolinite
Hematite Bauxite
Mineral Environments of Formation
Gold that has been liberated by weathering and erosion get carried away by streams and deposit within placer deposits
Mineral Environments of Formation
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.
Mineral Environments of Formation
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
Minerals as Indicators of Ancient Environments