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Quartz

  Quartz   Quartz is hexagonal and commonly occurs as crystals ranging in size form microscopic to crystals weighing several tons. Where it crystallizes unhindered by other crystals, such as in cavities in rock or in a liquid containing few other crystals, it shows well-developed hexagonal prisms and sometimes showing apparent hexagonal pyramids or dipyramid. When it crystallizes in an environment where growth is inhibited by the surroundings, it rarely show crystal faces. It is also found as microcrystalline masses, such as in the rock chert, and as  fibrous masses, such as in chalcedony. Vitreous lusture.   As visible crystals, Quartz is one of the more common rock forming minerals. It occurs in siliceous igneous rocks such as volcanic rhyolite and plutonic granitic rocks. It is common in metamorphic rocks at all grades of metamorphism, and is the chief constituent of sand. Because it is highly resistant to chemical weathering, it is found in a wide variety of sedimentary r
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Basics of the Earth

 

The Earth has evolved (changed) throughout its history, and will continue to evolve.

􀁺 The Earth is about 4.6 billion years old, human beings have been around for only the past 2 million years.

􀁻 Thus, mankind has been witness to only 0.043% of Earth history.

􀁻 The first multi-celled organisms appeared about 700 million years ago. Thus,

organisms have only been witness to about 15% of Earth's history.

The Earth has a radius of about 6371 km, although it is about 22 km larger at equator than at poles.

Density, (mass/volume), Temperature, and Pressure increase with depth.

 

Internal Structure of the Earth:

 

Earth has layered structure. Layering can be viewed in two different ways:

1. Layers of different chemical composition

2. Layers of differing physical properties.

 


Compositional Layering

 

􀁻 Crust - variable thickness and composition

􀂄 Continental 10 - 70 km thick - "granitic" (made mostly of Oxygen and Silicon) in Composition

􀂄 Oceanic 2 - 10 km thick - "basaltic" (less Silicon than in continental crust, more Magnesium)

􀁻 Mantle - 3488 km thick, made up of a rock called peridotite. Solid but can deform so that it confects (moves in response to temperature differences).

􀁻 Core - 2883 km radius, made up of Iron (Fe) and small amount of Nickel (Ni)

 

Layers of Differing Physical Properties

 

􀁻 Lithosphere - about 100 km thick (deeper beneath continents)

􀁻 Asthenosphere - about 250 km thick to depth of 350 km - solid rock, but soft and flows easily.

􀁻 Mesosphere - about 2500 km thick, solid rock, but still capable of flowing.

􀁻 Outer Core - 2250 km thick, Fe and Ni, liquid

􀁻 Inner core - 1230 km radius, Fe and Ni, solid

All of the above is known from observations that have been made from the surface of the Earth, in particular, the way seismic (earthquake waves) pass through the Earth as we will discuss later in the course.

The atmosphere is the outermost layer. It has the lowest density and consists mostly of Nitrogen (78%) and Oxygen (21%).

 

Composition of the Earth

The bulk chemical composition of the Earth is mostly Iron (Fe, 34.6%), Oxygen (O2, 29.5%), Silicon (Si, 15.2%), and Magnesium (Mg, 12.7%), with other elements making up the other 8%. These elements are distributed unevenly 

Due to the layering, with Fe being concentrated in the core, Si, O2, and Mg being concentrated in the mantle, and Si, O2, and the other elements being concentrated in the thin veneer of the crust.

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