I discovered an unusual combination a few days back: A somewhat petite barred olivine (BO-type) micrometeorite, NMM 4021, measuring approximately 0.2 mm with smooth surface and a large nickel-iron bead in the front. And on the side; a perfect pyramidal olivine (forsterite) crystal!
I assume that the pyramidal crystal growth on this enchanting micrometeorite started isolated in the glass when the micrometeoroid was still in a molten stage. It follows that the metal bead would have triggered crystallization backwards, and the temperature would have been about right for barred olivine growth. It’s funny that seven years ago, it was considered completely impossible to identify micrometeorites based on their visual appearance.
Today we not only know how to identify them, but can deduce the formation process! We can estimate the approximate peak temperature during atmospheric entry, speed, entry angle, and spin. The next would be to identify their parent bodies in space!
We recently published another article about micrometeorites with large metal beads, which I highly recommend. See you there?