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Schlieren "flames" |
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| Meteorite, Ysleta, Iron, ungrouped. |
| "Schlieren," a German term meaning "stria" or
"streak" (from Middle High German "slier"), is a versatile
descriptor used across various scientific fields, including geology,
petrography, optics, chemistry, metallurgy, meteoritics, fluid dynamics, and
biology. While its specific meaning can vary by discipline, it commonly refers
to lines or shapes that stand out due to differences in composition or texture
from their surroundings. In this context, "schlieren flames" are defined as irregular streaks or masses that transition gradually into the surrounding material. This term is applied to the Ysleta meteorite, an ungrouped iron meteorite found in Texas, USA. Ysleta is polycrystalline iron with a plessitic matrix-a fine mixture of alpha-iron and gamma-iron phases. Polished sections reveal no clear macrostructure, but light etching exposes numerous parent austenite grains, each roughly 1-2 cm in diameter. As the high-temperature austenite began cooling and transforming into kamacite, nucleation initiated along grain boundaries. Buchwald describes these boundaries as "delicate," appearing as kamacite veins only 10-50 microns wide. Further cooling transformed the austenite into micron-scale plessitic mixtures. Within millimeter-sized regions, "schlieren flames" emerge-not as simple lines, but as distinct, flame-like shapes visible amid the matrix. |
Figure 1. Scale bar 600 µm. |
| Ysleta, Iron, ungrouped. |
| Flame shaped structures (primary, forming during nucleation of austenite to kamacite). The flame shapes occur within millimeter-sized, fine grained duplex mixtures (populations) of alpha-iron and gamma-iron. |
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