Matijevic Hill first survey, Sol 3057 - 3152 |
Matijevic Hill first survey, Sol 3057 - 3152 |
Aug 31 2012, 09:19 AM
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The Poet Dude Group: Moderator Posts: 5551 Joined: 15-March 04 From: Kendal, Cumbria, UK Member No.: 60 |
Oooooh, you're pretty...
Might be here a while, you think? Edit: better colours on this amended version, I think... http://twitpic.com/apn9s1/full -------------------- |
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Sep 8 2012, 02:54 PM
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#2
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Member Group: Members Posts: 282 Joined: 18-June 04 Member No.: 84 |
Does anyone know of a cross section of a tektite? This is the only image I could find online:
http://www.panoramio.com/photo/3894593 The latest MI shot shows the cross section structure a bit better http://qt.exploratorium.edu/mars/opportuni...M5P2935M2M3.JPG They do bear a superficial similarity to the very last image on this page http://www.meteorite-times.com/Back_Links/...te_of_Month.htm |
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Sep 8 2012, 07:34 PM
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#3
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Member Group: Members Posts: 384 Joined: 4-January 07 Member No.: 1555 |
Tektites are glassy bits of impact melt that hardened in the air; their shape need not be spherical, and they are probably irrelevant to the subject of this discussion. Lapilli are gravel-sized fallen melt stones, without reference to specific shape or origin (only size), and the term alone therefore is ambiguous.
As is being discussed, there are many types of spherules and other intrinsically rounded objects, of various origins. Spherules formed by some combination of chemical and physical accretion, such as concretions (formed by pure chemical accretion owing to abrupt changes in chemical properties of groundwater that reduce mineral solubility) and accretionary lapilli (formed by a combination of condensation and physical accretion - possibly involving electrostatic charge - of particles in a turbulent, cooling and mixing gas cloud, and thus not unlike hailstones in concept) are NOT HOLLOW on the inside, unless perhaps internally weathered or altered (as most are on Earth). The spherules under discussion, or at least many of them, ARE distinctly hollow, and some appear to have objects in their center. This feature (hollow, possibly with junk on the inside) is characteristic of spherules formed by devitrificationof a hot hydrous glass, especially of the variety called lithophysae. As microcrystallites of anhydrous silicate minerals grow radially outwards, in many cases around a central object or megacrystal that served as a nucleus, they release steam that can inflate the spherule as it grows, leading to a hollow inside (except perhaps for the remant central object). The images haven't shown any yet, but some lithophysae even develop an onion-like or layered outer structure (but with open space between the layers), as a rind of crystallites develops, then steam escapes past it, inflating the still soft hot glass, then another rind of crystallites grows, and so on. Oppy may have been imaging impact glass cementing breccia ever since it arrived at Cape York. Martian impact glasses and melts, compared to those found elsewhere, should be especially hydrous and full of salts, both of which characteristics would favor devitrification (crystallization), so finding spherules formed by devitrification of hot glass or melt shouldn't be surprising. I repeat, this is just one suggestion among many, and need not be correct, but it appears to be the only one so far that accounts for the intrinsically hollow structure with junk inside and an apparent rind on the outside that has just been imaged here. Greater magnification revealing a concentric outer rind of microcrystallites (as mentioned by Bill Harris above), or new images revealing a separated outer onion-skin structure, both would support the hypothesis. I hope this background information helps the discussion. |
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Sep 8 2012, 08:09 PM
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#4
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Senior Member Group: Members Posts: 3516 Joined: 4-November 05 From: North Wales Member No.: 542 |
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