VEINS

-Fractures filled with a minerals that precipitated from solution

-Common precipitated minerals:

   quartz, calcite, zeolite, chlorite, ore minerals

Origin of Veins:

http://www.structural-geology-portal.com/animations.html

Joints                

Shear ruptures

Vein Array- group of veins in a rock body.

    Non-Systematic Vein Arrays- 

        non-planar veins that vary in width and orientation

    Planar Systematic Vein Array- 

        planar, parallel, regularly spaced veins

    En Echelon Vein Arrays- 

        short, offset sub- parallel veins 

        lie between two parallel enveloping surfaces 

        inclined at an angle to enveloping surfaces.  

    Stockwork Veins- 

        -cluster of irregularly shaped veins of 

        -highly variable orientation 

        -occur in a pervasively fractured rock body.

Vein Filling:

            Blocky (sparry)-  

            -equant vein filling crystals 

            -may display euhedral crystal faces

Blocky, euhedral crystal forms in a granitic vein which cross-cuts syenite, Mosinee, Wisconsin

Fibrous- characterized by fibrous (linear) mineral growth.

  - fibrous- high (>10:1) length:width ratio

    -may develop by repeated cycle of �crack and seal�

   -mechanism whereby elevated fluid pore pressures crack  a vein, followed by sealing from mineralized solution.

    -may be useful for strain analysis  

Syntaxial Veins-

-vein fill is usually same mineral composition as the wall rock.

-Cracking occurs in the center of the veins  

http://www.structural-geology-portal.com/syntaxial_growth_animation.html

Step 1: Cracking along center        

Step 2: New crack along the center

Antitaxial Veins- -veins may be of different mineral composition than host rock. Cracking occurs between host rock & vein material

http://www.structural-geology-portal.com/antitaxial_growth_simulation.html

Step 1- Tensional cracking

Step 2- shear cracking

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