Vaca Muerta is actually a mesosiderite: a stony-iron meteorite characterized as a mixture of core, mantle, and crustal material, all mixed together by a massive impact ~4.5 billion years ago.
This is a center slice from one of the largest eucritic clasts found in Vaca Muerta. It appears to be a monomict impact melt breccia.
For more information on these interesting clasts, see: Diverse eucritic pebbles in the Vaca Muerta mesosiderite, by Alan Rubin and Eric Jerde (1987).
This slice tips the scale at 55 grams, and measures about 5 x 7 cm.