Failed cast silicon.
An example of the element Silicon

This is a mistake from a university research laboratory- someone was trying to melt some high purity silicon into a crucible, probably graphite. The melter they were using employed a vacuum/argon electric arc melting chamber, with a vacuum-suction casting attachment below where a trap door opens below the main melting chamber and your molten material is sucked down into the crucible (hopefully).

For whatever reason, it didn't work in this case. You can see the crucible shape in the really rough, unhappy looking bottom, where the solidification occurred too rapidly. However, on the top is a beautiful crystalline display, showing both the purity of the material and the tendency of silicon to crystallize, even when solidification occurs rapidly, which it likely did in this case.