Calama 074 is a 17 gram oriented ordinary chondrite found in October 2018 by Ilya Kryachko on a limestone plateau 40 km east of the city of Calama, Chile. Calama is in the Atacama desert at 2,260 m elevation. Average annual rainfall quotes differ wildly. Wikipedia gives 5 mm with no citation. Sources say that no rain at all fell from 1903 to 1918 (or from 1602 to 1941) (or from 1570 to 1971). The place is arid. Details are sketchy.
In his Meteorite Picture of the Day posting Timur Kryachko, Ilya’s brother, states that both the front and rear of this oriented meteorite retain thick fusion crust. In recent correspondence Timur avers that a portion of the leading face may be free of crust. I suggest that oriented flight was not fully stable and that some in-flight rocking motion distributed melt rather broadly. Timur Kryachko photo.
Timur made the thin section from this cross-section illustrated in his MPOD. The stone was small, about 36 mm long. Timur Kryachko photo.
Standard glass slide 26 mm x 46 mm. The front of the meteorite is to the right. Transmitted light.
Closer views of these two areas are below. Thin section in transmitted light.
The back has a thick vesiculated fusion crust. The melted crust overlies a heat affected substrate. Thin section in plane polarized light (PPL). Field of view (FOV) is 5 mm wide
Here the front appears to have shed all of its melt. It has a deeper heat affected zone than the back of the stone. Thin section in PPL. FOV 5 mm wide.
Below are panoramas of the fusion crust in each of these zones, in both PPL and cross-polarized light (XPL). The first three images are details from the panoramas.
