Partial melting
Partial melting is when only part of a rock melts, producing a melt with a different composition from the solid left behind.
Rocks are mixtures of minerals that melt at different temperatures, so when a rock is heated it does not melt all at once. Partial melting produces a small amount of liquid enriched in elements that do not fit easily into the remaining crystals, leaving a solid residue depleted in them.
In asteroids, partial melting was an early step towards full differentiation. The primitive achondrites capture this stage. Acapulcoites lost a little iron sulfide melt, while lodranites lost both metal-sulfide and silicate melts, leaving a coarser-grained residue. Ureilites and brachinites are also thought to be residues of partial melting, and winonaites record it too.
On larger bodies, partial melting of the mantle produced the basaltic magmas that erupted as lavas. Eucrites on Vesta and shergottites on Mars are thought to be products of melting deep in their parent bodies. Comparing residues and melts helps estimate how hot an asteroid became and how quickly.
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