1 / 21

Sedimentary Petrology

Sedimentary Petrology. Morgan Schaller. Some Properties of Light:. polarization. Some Properties of Minerals:. All minerals aside from those in the cubic system are termed anisotropic and have a preferred orientation where light travels faster than in other directions.

michaela-sweetman
Download Presentation

Sedimentary Petrology

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Sedimentary Petrology Morgan Schaller

  2. Some Properties of Light: polarization

  3. Some Properties of Minerals: All minerals aside from those in the cubic system are termed anisotropic and have a preferred orientation where light travels faster than in other directions

  4. Some Properties of Light: All anisotropic minerals have some component of double refraction, but it is especially pronounced in optical calcite (or Icelandic spar).

  5. Optical PropertiesA: Plane Polarized Light 1) Color: Most minerals are colorless under PPL, but some minerals are intensely colored. As a general rule, dark colored minerals in hand specimen (e.g., pyroxene, amphibole, biotite etc.), are colored in PPL. Light colored minerals (quartz, fluorite, feldspars, muscovite etc.) are colorless.

  6. Optical PropertiesA: Plane Polarized Light 2) Pleochroism: This is an interesting phenomenon where anisotropic minerals appear to change color as they are rotated in PPL. It has to do with variable indices of refraction and is related to the crystal class of the minerals.

  7. Optical PropertiesA: Plane Polarized Light 3) Cleavage: Get your minds out of the gutter. Same property as seen in hand specimen, but you are now looking at 2 dimensional slices.

  8. Optical PropertiesA: Plane Polarized Light 4) Relief: the ratio of the index of refraction of a mineral to the index of refraction of the material immediately adjacent to it (usually glass).

  9. Optical PropertiesA: Plane Polarized Light 5) Crystallinity: A crystal with sharp, geometric edges is said to be euhedral. One that has rounded edges (e.g., water abraded) is said to be anhedral.

  10. Optical PropertiesB: Crossed Nichols (XN) 6) Extinction: occurs when the indicatrix aligns up with the polars and the entire crystal goes black (extinct). PPL XN

  11. Optical PropertiesB: Crossed Nichols (XN) 7) Birefringence. This is the most important property of minerals under crossed polars. Light is split into two beams, at right angles to one-another. These colors are ‘interference colors.’ PPL XN

  12. Optical PropertiesB: Crossed Nichols (XN) 8) Optical Twinning. Two or more crystals of a single mineral grow together in a mathematically predicable pattern (involves twin planes, twin axes etc). These patterns show differences under crossed polars. PPL XN

  13. Optical PropertiesB: Crossed Nichols (XN) 9) Zonation. Some minerals change their composition has they grow, particularly those that that form continuous series through solid solution during igneous processes (e.g., olivine, plagioclase). This can result in optical zonation. PPL XN

  14. Cementation: Cementation: pore-filling minerals precipitated into voids within sediment/sedimentary rocks. Matrix: fine-grained* material deposited simultaneously with larger particles. Generally appears as darker-colored detritus between grains Cement: a chemical precipitate between grains formed from pore-water long after deposition.

  15. Cementation: • Cementation: pore-filling minerals precipitated into voids within sediment/sedimentary rocks. • Common Cements: Quartz Hematite Calcite Chert Limonite Aragonite Chalcedony Phosphate Mg-Calcite Opal Clay Dolomite Glauconite Siderite etc.

  16. Cementation: Homogenous Chemically pure Lines pores Specific fabrics Multiphased Zoned  SEM Cement Qtz grains

  17. Cementation: Homogenous Chemically pure Lines pores Specific fabrics Multiphased Zoned  SEM Hematite Cement Qtz Cement

  18. Cementation:

  19. Cementation:

  20. Composition of sedimentary rocks depends on: Mineral availability – cannot form an arkose from weathering paleozoic limestone Mechanical durability of the mineral – high hardness and durability is selected by longer periods of abrasion. Not much feldspar at the beach… Chemical stability – Those minerals that crystallize from a magma at lower temperatures are more stable… Almost the reverse of Bowen’s reaction series:

  21. Procedure: • Three groups of slides, look at one from each. • First look over the whole slide with low power • Find an interesting area, switch to a higher magnification – record this magnification • Sketch the field of view – NO PEN! • ID sed structures + grain contacts • Estimate mean grain size • Estimate sorting • Assign a depositional environment • Name the rock

More Related