Reprecipitation sites

Reprecipitation is an important part of the deformation process. There are several different sorts of site such as veins... which can occur on all scales.

outveins
Vein arrays seen on a bedding surface in Cretaceous limestones, Sdanetsch, Swiss Alps. These veins are filled by new, bright white calcite.

They can often form across large parts of an outcrop ->

veints
Photomicrograph of a calcite vein developed in a limestone, from the french Alps (Chartreuse area). This vein is about 100 microns across.

and be found in thinsection <-.

Veins are simply voids formed by dilatation created along fractures (commonly tensile fractures) into which has been precipitated new minerals - such as calcite or quartz.



pyrite
Photomicrograph of fibrous reprecipitation of calcite around a "rigid" pyrite grain. These features are called pressure shadows or pressure fringes. The calcite comes from the host rock which has dissolved from the plane of vein. This material was collected from strongly deformed Jurassic limestones, Beaufortain, NW French Alps.

But there are other forms of precipitation site such as pressure shadows -> .

There are also special vein arrays called tension gashes.

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