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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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FOSSIL AND FOSSILIZATION

                                                              FOSSILS AND FOSSILIZATION

 

                                                                    figure 1.1 Trilobite 


FOSSIL :-

Fossils are the preserved remains of plants and animals whose bodies were buried in sediments, such as sand and mud, under ancient seas, lakes and rivers. It can be any preserved remains like impression, or trace( bones, nails, teeth etc.) of any once-living thing from a past geological age.

Examples : petrified wood, microfossil (foraminifera) etc.

FOSSILIZATION :-

A very small amount of prehistoric life got fossilized. For this phenomenon to take place various conditions are needed. Mostly the hard parts of an organism can become fossilized, such as teeth, claws, shells, and bones. The soft body parts are usually lost, except for in very special conditions.

CONDITIONS AND NEEDS FOR FOSSILIZATION:-

• Fossils only occur in sedimentary rock, no others. The best scenario would be in which an organism is buried at the bottom of a lake where it is then covered by a lot of sediment. In this type of environment, the organism is protected from other animals and natural elements that would cause the body's breakdown. It is crucial that the body be in an environment that allows for rapid burial. Areas in which there is a high rate of sediment deposition is ideal because of the presence of minerals and the increase of pressure.

• For fossilization of soft parts non oxygenated place are needed because in presence of oxygen dead organism may got chemically reacted and got decomposed. But in non-oxygenated places can preserve the soft part which can turn into petroleum after millions of years.

• Other ways of preservation- petrification. Most people have seen petrified wood. This is how it happened: Long ago, dead logs were washed into a river and buried in the sand. Water with alkaline and dissolved silica went down through the sediments, and contacted the logs. The logs decayed, releasing carbon dioxide, which dissolved in the water and formed carbonic acid. The alkaline water was then neutralized, and the silica precipitated out of the solution. Very slowly, the cellulose of the wood is replaced, molecule by molecule, by the silica. Eventually, the wood is replaced in perfect detail by minerals. If other minerals are there, also, the wood could be stained pretty colours.

• Organisms can also be preserved by carbonization. If a leaf falls into a stagnant, oxygen-poor swamp, it may not decay. If it gets covered in silt and subjected to heat and pressure, most of the leaf's organic material is released as methane, water, and carbon dioxide. The remainder is a thin film of carbon, showing the imprint of the leaf. Insects and fish can be preserved in this way too.


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