Skip to main content

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
Post a Comment

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.)


Location: No.65, 4th Cross Rd, Kamarajapuram, Karur, Tamil Nadu 639002, India

Comments

Post a Comment

Popular posts from this blog

Types Of Metamorphic Textures

  STRUCTURES OF METAMORPHIC ROCKS (MACROTEXTURES): (i)                 Slaty cleavage : A pervasive, parallel foliation (layering) of fine-grained platy minerals (chlorite) in a direction perpendicular to the direction of maximum stress. It produces the rocks slate and phyllite. (ii)           Schistose : Schist has a lepidoblastic foliation if this foliation is defined by oriented mica, and a nematoblastic foliation if such a foliation is defined by the orientation of prismatic minerals as amphiboles and pyroxenes. (iii)        Gneissic :   A complex banded texture made of schistose layers or bands alternating with bands commonly characterized by a granoblastic texture. (iv)            Granoblastic: Granular, interlocking equi-dimensional grains of subequal size; no preferred orientation or cleavage. (v)              Hornfelsic : Fine-grained, granular interlocking grains, possibly of variable shapes and sizes. No preferred orientation. (vi)              Cataclastic : •
Post a Comment
Read more

TEXTURES OF CLASTIC SEDIMENTARY ROCKS

TEXTURES OF CLASTIC SEDIMENTARY ROCKS           When sediment is transported and deposited, it leaves clues to the mode of transport and deposition. For example, if the mode of transport is by sliding down a slope, the deposits that result are generally chaotic in nature, and show a wide variety of particle sizes. Grain size and the interrelationship between grains gives the resulting sediment texture. Thus, we can use the texture of the resulting deposits to give us clues to the mode of transport and deposition.   Figure 1.1 - Type of sorting Sorting :-   The degree of uniformity of grain size. Particles become sorted on the basis of  density, because of the energy of the transporting medium. High energy currents can carry larger fragments. As the energy decreases, heavier particles are deposited and lighter fragments continue to be transported. This results in sorting due to density. If the particles have the same density, then the heavier particles will also be larger,
Post a Comment
Read more

HYDROTHERMAL ORE DEPOSITS

  HYDROTHERMAL ORE DEPOSITS                                                   Figure 1.1 HYDROTHERMAL PROCESS     Concentration by hot aqueous (water-rich) fluids flowing through fractures and pore spaces in rocks.   The fluid temperature ranges from 50 to 500 degree C. These fluid can be the final product of volcanic differentiation or the ground water got heated by contact of magma or chamber.   Hydrothermal deposits are produced when groundwater circulates to depth and heats up either by coming near to the hot igneous body at depth or by circulating to great depth along the geothermal gradient.   Such hot water can dissolve valuable substances throughout a large volume of rock. As the hot water moves into cooler areas of the crust, the dissolved substances are precipitated from the hot water solution. If the cooling takes place rapidly,  T hey might occur in open fractures or upon reaching a body of cool surface water, then precipitation will take place over a limi
3 comments
Read more