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  1. #61
    Senior Member Stevo's Avatar
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    Quote Originally Posted by Synapse View Post
    I'm with Perfectgirl would you expand on some of the terminology.
    Stratigraphic boundary
    Purslane Formation.
    Bedding planes.
    Small-scale folding.
    Centimeter-scale folding.
    Meter-scale anticline.
    Tectonic foliation.
    Foliation planes.
    All right. I'll explain these concepts the best I can. My work in this field assignment was mostly to analyze and map structures and patterns in the sedimentary rocks found around Western Maryland. Sedimentary rocks are the most common type of rock exposed at the surface of the earth---they are formed by the gradual deposition and cementation of small particles of rock over long periods of time. Because of how they form, they are always originally deposited in horizontal layers stacked on top of one another. One unit of sedimentary rock is called a bed, and the study of how these beds overlay one another is called stratigraphy. Several beds together are collectively referred to as Strata, and the boundary between two beds is known as a stratigraphic boundary.

    Now, although sedimentary rocks are always deposited in horizontal planes, it is very rare to find exposed sedimentary rocks in the field in nice flat layers. Usually, the geological forces behind Plate Tectonics exert themselves on the sedimentary layers and they become deformed. Sometimes this just means that the layers are tilted a bit but still retain their "flatness", if you will. That is what I am referring to when I say "bedding planes". Other times, the rocks and the layers that make them up are completely deformed, and are no longer in straight flat layers. This phenomenon is called Folding. There are several basic types of folds, but the two most common are called synclines and anticlines. Here's a simple picture that illustrates these folds:



    These sedimentary layers were originally flat, but compressional forces squeezed them together so that they became crushed and folded against each other in that manner. If you look in the photos I provided, you'll see a lot of examples of folding in pictures 3-7. What I am referring to when I say "small-scale folding" or "centimeter-scale folding" is simply the relative size of the fold. Some folds can be tiny, and you can measure the distance from the limbs, or the two sides of the fold, in centimeters. On the other hand, some folds can be kilometers and kilometers across, such as the ones in the Appalachian Mountains near my home.

    Tectonic foliations are a bit tougher for me to define. A tectonic foliation is a uniform planar deformation that comes about as the result of weak metamorphism in the original sedimentary rock. Under great heat and pressure, driven by tectonic forces in this case, sedimentary rocks will begin to rearrange themselves and recrystallize into new forms of rocks. This recrystallization will realign the orientation of the rocks so that you can identify uniform patterns in the rocks themselves roughly aligned to the same plane. I'm sorry if that's a bit technical and hard to understand, but if you look carefully at my last picture, you will see that the rock seems to have a wrinkled surface, and all these wrinkles are aligned in the same way in a plane that is rather close to horizontal. That is a tectonic foliation.


    Is geology an earth science? Are there different fields in geology? Are there different crystals and rock formations. I'm interested in learning more about this and your in the field so to speak. How did you get into wanting to become a geologist? Are there different types of crystals and rock formations and how do they form?

    I know asking too much. Thanks for the great photos.
    Geology is not just an Earth science, it is the earth science. It is the study of the Earth and its natural processes. It covers several fields: Vulcanology, the study of Volcanoes---my main interest---Petrology, the study of igneous and metamorphic rocks, Sedimentology, the study of sedimentary rocks, Mineralogy, the study of minerals, Seismology, the study of earthquakes, and Paleontology, the study of extinct life, are some of them. I was always interested in rocks and minerals, and chiefly volcanoes, and when I found out through a serendipitous college visit that you could study these things as your career, I knew immediately that that was what I wanted to do. I'm not exactly sure what you mean when you ask "are there different crystals and rock formations", but if you have any other specific questions, I'll be happy to answer them the best I can.

  2. #62
    Senior Member Synapse's Avatar
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    Quote Originally Posted by Stevo View Post
    Geology is not just an Earth science, it is the earth science. It is the study of the Earth and its natural processes. It covers several fields: Vulcanology, the study of Volcanoes---my main interest---Petrology, the study of igneous and metamorphic rocks, Sedimentology, the study of sedimentary rocks, Mineralogy, the study of minerals, Seismology, the study of earthquakes, and Paleontology, the study of extinct life, are some of them. I was always interested in rocks and minerals, and chiefly volcanoes, and when I found out through a serendipitous college visit that you could study these things as your career, I knew immediately that that was what I wanted to do. I'm not exactly sure what you mean when you ask "are there different crystals and rock formations", but if you have any other specific questions, I'll be happy to answer them the best I can.
    Thank you for explaining. There are days when I am delayed in my responses. Lets see.

    Petrology

    +


    Vulcanology

    +


    Sedimentology

    +


    Mineralogy

    +


    Seismology

    +


    Paleontology

    +


    When words are missing I express visually.

    What I mean by different crystals is that there are metallic, ionic and molecular crystal formations. And cubic or isometric, tetragonal, orthorhombic, hexagonal, trigonal, triclinic and monoclinic types of crystals. You've helped me identify what I was focusing on there, mineralogy.

  3. #63
    Senior Member Stevo's Avatar
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    Quote Originally Posted by Synapse View Post
    What I mean by different crystals is that there are metallic, ionic and molecular crystal formations. And cubic or isometric, tetragonal, orthorhombic, hexagonal, trigonal, triclinic and monoclinic types of crystals. You've helped me identify what I was focusing on there, mineralogy.
    Yes, judging by your posts in this topic I would say your principle interest is in mineralogy. Unfortunately that is probably the area of geology I have the least experience in right now. As a student, I don't yet have the luxury of picking and choosing the course material I want to learn.

  4. #64
    Symbolic Herald Vasilisa's Avatar
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    zomg, you left out the glamorous and lucrative (:rolli field of hydrogeology!



    There exist literal seas beneath our feet, Synapse, seas.
    the formless thing which gives things form!
    Found Forum Haiku Project


    Positive Spin | your feedback welcomed | Darker Criticism

  5. #65
    Senior Member Stevo's Avatar
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    Yeah, there's groundwater studies too. Not my personal favorite, but I'll be taking a course on it next semester.

  6. #66
    Senior Member Synapse's Avatar
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    That reminds me of geothermal energy and geomorphology, well those words popped into my mind and then something about the environment I studied once, I'll have to go look for it, forgot.

  7. #67
    Senior Member Synapse's Avatar
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    I've been distracted and needs to find stuff about stuff for now finds stuff about stuff. lol


    Types of crystals
    1 Cubic or Isometric - not always cube shaped! You'll also find octahedrons (eight faces) and dodecahedrons (10 faces).
    2 Tetragonal - similar to cubic crystals, but longer along one axis than the other, forming double pyramids and prisms.
    3. Orthorhombic - like tetragonal crystals except not square in cross section (when viewing the crystal on end), forming rhombic prisms or dipyramids (two pyramids stuck together).
    4. Hexagonal - six-sided prisms. When you look at the crystal on-end, the cross section is a hexagon.
    5. Trigonal - possess a single 3-fold axis of rotation instead of the 6-fold axis of the hexagonal division.
    6. Triclinic - usually not symmetrical from one side to the other, which can lead to some fairly strange shapes.
    7. Monoclinic - like skewed tetragonal crystals, often forming prisms and double pyramids.

    Groups of crystals
    1. Covalent Crystals - A covalent crystals has true covalent bonds between all of the atoms in the crystal. You can think of a covalent crystal as one big molecule. Many covalent crystals have extremely high melting points. Examples of covalent crystals include diamond and zinc sulfide crystals.
    2. Metallic Crystals - Individual metal atoms of metallic crystals sit on lattice sites. This leaves the outer electrons of these atoms free to float around the lattice. Metallic crystals tend to be very dense and have high melting points.
    3. Ionic Crystals - The atoms of ionic crystals are held together by electrostatic forces (ionic bonds). Ionic crystals are hard and have relatively high melting points. Table salt (NaCl) is an example of this type of crystal.
    4. Molecular Crystals - These crystals contain recognizable molecules within their structures. A molecular crystal is held together by non-covalent interactions, like van der Waals forces or hydrogen bonding. Molecular crystals tend to be soft with relatively low melting points. Rock candy, the crystalline form of table sugar or sucrose, is an example of a molecular crystal.

  8. #68
    Senior Member Synapse's Avatar
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    Crystallography

    Pasteur's work became the foundation for crystal polarimetry, a method by which light is polarized, or aligned to a single plane. It was soon discovered that other crystals were also capable of polarizing light. Today, crystal polarimetry is used extensively in physics and optics.

    Another phenomenon displayed by certain crystals is piezoelectricity. From a Greek work meaning "to press," piezoelectricity is the creation of an electrical potential by squeezing certain crystals.

    The piezoelectric effect also works in reverse: when an electrical current is applied to a crystal such as quartz, it will contract; if the direction of the current is reversed, the crystal will expand. If an alternating current is used, the piezoelectric crystal will expand and contract rapidly, producing a vibration whose frequency can be regulated. Because of their precise vibrations, piezoelectric crystals are used in radio transmitters and quartz timepieces.

    Perhaps the most important application of crystals is in the science of x-ray crystallography. In 1912, Laue perceived that the regular stacked-plane structure of a crystal would act like a very small diffraction grating; this hypothesis was successfully tested with a crystal of zinc sulfide, and x-ray crystallography was born. Using a crystal, scientists could now measure the wavelength of any x ray as long as they knew the internal structure of their crystal. Also, if an x ray of a known wavelength was used, the molecular structure of unknown crystals could be determined. Since that time, x-ray crystallography has been used to examine the molecular structure of thousands of crystalline substances and was instrumental in the analysis of DNA. Crystallography remains an important branch of earth science because the analysis and study of crystals often yields important information concerning the type and rate of geological processes.

  9. #69
    Senior Member Synapse's Avatar
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    Interesting stuff.

    [youtube="HEheh1BH34Q"]Star Size[/youtube]

    Hahaha it is so about rocks...bigger rocks than earth, erh, okay bigger masses than earth. Whoah!

  10. #70
    A window to the soul
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    I made a quartz radio with my Dad when I was kid. I couldn't believe it, like magic it worked.
    I've heard crystals have healing properties too. Have you heard this?

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