In this post, I’m pleased to introduce you to a rare variety of porphyritic olivine (PO) type micrometeorites that were first discovered by the Concordia Team in Antarctica 21 years ago. This special variety has a matrix of translucent glass with myriad small olivine crystals composed of forsterite forming inside.
NMM 2851 is a remarkable micrometeorite of the same habitus, which was discovered by yours truly on a flat roof in Sarpsborg, Viken, Norway in the autumn of 2021. Measuring approximately 0.3 mm, it has quite a striking appearance; Under the light microscope you mainly see the crystals inside the glass, while the scanning electron microscope (SEM) image reveals some crystal faces on the surface.
Also on the surface there are patches of sulfide that appear as white “craters” on the backscatter SEM image. These remarkable characteristics were formed from the degassing of volatiles during the space gem’s journey through the Earth’s atmosphere.
Because of characteristics consistent with other “barely melted” micrometeorites, we know this spherule experienced a relatively low peak temperature during the atmospheric entry. Also, because the sulfide is intact and has not been weathered away, we know this particular micrometeorite has a very short terrestrial age.