Atlantis Online
March 28, 2024, 08:23:08 am
Welcome, Guest. Please login or register.

Login with username, password and session length
News: Satellite images 'show Atlantis'
http://news.bbc.co.uk/1/hi/sci/tech/3766863.stm
 
  Home Help Arcade Gallery Links Staff List Calendar Login Register  

Metamorphism

Pages: 1 [2]   Go Down
  Print  
Author Topic: Metamorphism  (Read 1683 times)
0 Members and 30 Guests are viewing this topic.
Rebecca
Superhero Member
******
Posts: 5201



« Reply #15 on: May 29, 2007, 11:31:28 pm »


Metamorphic textures are either granular or foliated. Here we examine only the foliated types.

    Foliation - any planar set of minerals, or banding of mineral concentrations, especially the planar structure that results from flattening of the mineral grains, like micas.

      Most Metamorphic rocks form in the influence of a directed stress field. Because of this they develop conspicuous directional textures. For example, the top illustration to the right shows the stress field before application (arrows), with the mineral grains randomly oriented. As metamorphism proceeds, the sheet structure silicates (flat minerals with basal cleavage) such as mica (biotite and muscovite) and chlorite start to grow. The sheets orient themselves perpendicular to the direction of maximum stress. The new parallel mineral flakes produce a planar texture called foliation. (from the Latin folium - leaf). Foliation can be subtle or pronounced depending on the degree of metamorphism.
     The foliated textures develop in the sequence listed below as temperature and pressure increases. Here we just define the textures. Below are descriptions and illustrations of how each texture develops.

Slaty cleavage - a pervasive, parallel foliation (layering) of fine-grained platy minerals (chlorite) in a direction perpendicular to the direction of maximum stress. Produces the rocks slate and phyllite.

Schistosity - the layering in a coarse grained, crystalline rock due to the parallel arrangement of platy mineral grains such as muscovite and biotite. Other minerals present are typically quartz and feldspar, plus a variety of other minerals such as garnet, staurolite, kyanite, sillimanite.

Mineral Banding (Gneiss) - The layering in a rock in which bands or lenses of granular minerals (quartz and feldspar) alternate with bands or lenses in which platy (mica) or elongate (amphibole) minerals predominate.


Report Spam   Logged
Pages: 1 [2]   Go Up
  Print  
 
Jump to:  

Powered by EzPortal
Bookmark this site! | Upgrade This Forum
SMF For Free - Create your own Forum
Powered by SMF | SMF © 2016, Simple Machines
Privacy Policy