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

From: Michael Farmer <mike_at_meteoritecentral.com>
Date: Tue, 21 May 2013 16:40:01 -0500
Message-ID: <4A411A18-1F3B-44A6-8022-C3EE12559DBD_at_meteoriteguy.com>

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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Received on Tue 21 May 2013 05:40:01 PM PDT