You raise a couple questions about geologic structures so here is the scoop and why. These photos are not an example of "slickenside". Zag, however, has the definitive example of slickenside found within a meteorite. a slickenside appears polished--hence the term "slick". For an enlarged photo of Zag slickenside <http://www.caillou-noir.com/TM2/image/Zag128400Aslickbzoomweb.jpg> or <http://www.caillou-noir.com/TM2/CGZag.htm> for the main page
Terrestrial slickenside can be very thin or not, undulating, and can run for the length of a fault. In meteorites, they are much thinner, form rapidly-- or in theory, by successive slips caused by successive collisions, as opposed to forming over time during fault slippages such as would be the case on Earth. It can undulate depending on the axis one views it. It is filled with a micro vein of reconsolidated "rock flower"or --debris dislodged in the grinding process of the two adjacent surfaces slipping by each other. Meteoritical slickenside such as in Zag resembles a very thin vein of coal or carbonaceous shale. To my knowledge it doesn't contain glass such as maskenlite (which would indicate flash melting and shock rebounding). It is clearly formed by two surfaces slipping by each other.
As to shattercones...
The possibilities of "shattercone-like" structures in Tatahouine as been discussed before with no conclusions. Recently a study was conducted on Tatahouine that found blebs of Alpha-crystobalite (a low temperature but high temperature polymorph of quartz). This perhaps indicates a low shock stage which tends to rule out shattercones. On the other hand, there were clues to a shock stage 5 followed by "annealing" which would have reabsorbed the laminae we would expect to find in sheared surfaces which might favor a shattercone effect. If there are shattercones in this meteorite they are not in a form as we know them on earth.
What you are likely seeing in your specimen is the striation/laminae of the "enstatite twinning law". Striations are superficially similar but distinctly different structures to shattercones. In mineralogy, certain minerals tend to follow patterns within a given mineral. A twin is two or more crystals growing within each other.(still called a twin even if it is a triplet). Sometimes they cross, sometimes they grow interlaced like a deck of cards shuffled into each other. This interlaced form is what enstatite follows. This meteorite is composed of an orthopyroxene (inosilicate series) at a ratio of Enstatite75%:Mg2 Si2 O6 and Ferrosilite25%: Fe2 Si2 O6. Enstatite is known for a laminate twining/striations.
As I understand it-- with cleavage plans at 87° or so, the enstatite plates are orientted back to back ( think of stacking playing cards face to back and looking at the whole deck from the side. What you are seeing is the truncated cleavage planes edge on. If you looked down the edge, parallel to the laminae, under a microscope, the edge would look like the teeth of a saw blade. To further complicate the observation, Tatahouine appears sort of homogeneous-what might be called in mineralogy "massive". In fact it seems to be composed of large intergrown and extensively orientated enstatite crystals. This may contribute to the appearance of a shattercone look when trying to trace the striation lines from one surface to another. We don't ordinarily see a fragment large enough to see a zig-zag-zig-zag as in a line of toppled dominoes. We only see closely spaced "zigs"in different planes so they look like they are converging toward a point.
Regards, Elton
Steve Witt wrote:
Greetings List,
Slickensides has been a topic brought up many times on the list. I'm still not exactly clear on what this is and I'd like to get a clarification. I recently acquired a small fragment of Tatahouine from Anne Black at Impactika. Besides having some fusion crust the specimen shows striations very similar to those seen in shattercones.
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