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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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Meteorites

Meteorites - chunks of rock from space that land on Earth.

Meteors are not meteorites Like meteorites, meteors are objects that enter Earth's atmosphere from space. But meteors-which are typically pieces of comet dust no larger than a grain of rice-burn up before reaching the ground.



Common minerals in meteorites:

·       kamacite,

·       taenite (both Ni-Fe alloys, different crytall structures)

·       pyroxene (especially bronzite)

·       olivine

·       plagioclase

 

Kinds of meteorites:

v irons

v stones

v stony-irons

 

Iron meteorites:

Predominantly Ni-Fe alloys

Minor amounts of other minerals such as troilite (FeS)

Types classified according to % Ni:

Hexahedrite octahedrite (has Widmanstatten structure, exsolution feature formed by slow cooling) ataxite

 

Stone meteorites:

Chiefly silicates, mostly ferromagnesian Up to 1/4 metallic Ni-Fe

 

Types:

Chondrites

Achondrites

 

Chondrites: Contain chondrules (BB-sized round bodies)

Composed chiefly of silicates such as olivine, pyroxene, and

plagioclase or glass Important type is carbonaceous chondrite.

High content of volatiles, including water and nonbiogenic

carbon (will later show how determined to be non-biogenic)

Have same composition as Sun's atmosphere

 

Achondrites: no chondrules

Same composition as terrestrial mafic and ultramafic rocks

Most achondrites are breccias

 

Stony-iron meteorites: Equal amounts of silicates and Ni-Fe

Alloys Many are crystallized silicates which have been brecciated, then invaded by metallic and sulfide melts

 

Classified according to kind of silicate:

pallasite (olivine)

mesosiderite (plagioclase, pyroxene) 


Moon:



basalt maria (with extra Fe and Ti)

anorthosite highlands

4 most common moon minerals:

pyroxene (augite and others)

plagioclase (Ca-rich)

olivine (Mg-rich)

ilmenite (iron titanium oxide)

No hydrated minerals.

No minerals formed by chemical weathering or life processes.

Depleted in volatiles (probably as a result of how Moon was formed.)


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