[meteorite-list] Chelyabinsk - slickensides or shock planes?

[Michael Farmer]

I found a very nice Chelyabinsk while running to the truck after finding a 1.2 kg stone. I saw it flash in the sun, a half stone with silver slickenside up, it was like a mirror.
Michael Farmer

Sent from my iPhone

On May 21, 2013, at 4:36 PM, "Bernd V. Pauli" <bernd.pauli at paulinet.de> wrote:

> Hello All,
> 
> We had a similar discussion many, many years ago
> (September 2001). Here's a short overview of our results:
> 
> Summary:
> 
> - broken surface is covered with glossy striations
> - slickensides are identified by shiny mirror like surfaces
>  on an otherwise rough rock
> 
> - they are the product of faulting in a rock body (as the crust
>  shifts, even slightly, the roughness of the rock tends to smooth)
> 
> - slickensides are formed from the movement of rocks relative to each other
>  along fracture planes in fault zones
> 
> - rub your finger along the grooves which make up the slickensides:
> 
> * they feel rough when you move your finger in the direction opposite
>  to which the adjacent rock moved to form the slickensides
> 
> + they feel smooth when you rub in the same direction the adjacent rock
>  moved because it sheared off any microscopic projections or rough
>  edges as it moved
> 
> => Not found in shatter cones!
> 
> - slickensides are formed when opposite sides of rock faults
>  move in different directions
> 
> - extreme pressure generates frictional heat as the rock faces are forced
>  past each other partially melting a thin veneer of rock at the interface
>  (result: smoothing of rough edges and a polished looking surface)
> 
> - they are not formed by explosive breakup in the earth's atmosphere
>  (in such a breakup pieces would be flying apart from each other
>  whereas in slickensides the opposite is happening: the rock faces
>  are being forced against each other) but: see below **
> 
> - possible formation scenario: an impact event in space results in
>  movement of two adjacent parts of  the stony meteorite relative to
>  each other along a preexisting fracture plane thus creating grooves
> 
> - slickensides are polished, grooved surfaces that occur along shear planes
> 
> - slickensides form along internal shear planes as opposite parts
>  move past one another
> 
> - opposite parts rub against each other, their surfaces become smoothed,
>  lineated, and grooved
> 
> - slickensides are formed when two planar sides grind past each other
> 
> - slickensides can be created at the moment of breakup (not by the explosive
>  part of this breakup but rather when two parts of the meteorite grind past
>  each other along a pre-    existing fracture – so-called shear rupturing) **
> 
> and here are some of the listees that participated in the discussion:
> 
> Charlie Devine (started the discussion), Eric Olson, Robert Verish,
> ... to name a few.
> 
> Cheers,
> 
> Bernd
> 
> 
> 
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