In a chunk of the meteorite EET 87720, found in Antarctic ice, lies a pink grain of sand. It's spinel, a mineral almost never seen in ureilites, and here it grew to half a millimeter. Such a find is like a time capsule from an early melt: it solidified when the parent body was just beginning to cool.
The oxygen isotopes in the spinel and neighboring olivine fall on the same line as those of other ureilites — meaning the grain wasn't captured from outside but grew on the same body. The crystallization temperature was estimated from the distribution of aluminum between minerals: 1318 ± 43 K. That's a hot furnace where the first aluminum melts were produced.
Why does this matter? Ureilites are almost devoid of feldspars — minerals rich in aluminum. It was thought that early aluminum melts were completely removed during partial melting. The discovered spinel is rare evidence that such melts existed and could survive locally.
The pink grain of sand survived melting, reduction, and shock compression. Now it tells the story of the parent body's first steps — how the first drops of aluminum magma were melted out of primitive material.
The spinel in EET 87720 is pink, a color visible even in polarized light — a rare sight in ureilites, where olivine and pyroxene usually dominate. A spinel grain 400–500 μm across can be compared to a grain of sand, but by ureilite standards it is a giant: typical accessory spinels in them are tens of times smaller.