78155 is a friable white cataclasite. It has been described as a holocrystalline, weakly-coherent, polymict breccia that was metamorphosed at a high temperature and has been grouped with other rocks from the early lunar crust as “feldpathic granulitic impactites”. 65% of 78155 is granoblasic matrix with another 20% crushed material. Small clasts of polygonal anorthosite have been reported. The overall mineralogical mode is ~75% plagioclase feldspar and ~25% mafic silicates (mostly pigeonite), with trace olivine, augite and opaques. Evidence for temperatures in excess of 1100°C during metamorphism are inferred from coexisting uninverted pigeonite and low-Ca augite, and from equilibrated olivine and ilmenite. Metallic iron and merrillite are also reported. Rotations 1 & 2 show the plagioclase-rich nature of the sample.
The sample weighed 401.1 grams before analysis and has been dated at 4.12±0.04 billion years (Ar/Ar).
Further details of this and other Apollo samples are here: http://curator.jsc.nasa.gov/lunar/
Apollo 17, the final manned landing mission, had two objectives: to obtain samples of ancient rocks from the lunar highlands and to look for evidence of younger volcanic activity on the valley floor.
This small Collection contains material deriving from both periods, including igneous rocks around 4.3 billion years old from the lunar highlands as well as younger volcanic samples dating from about 3.6 billion years ago.
Apollo 17 was launched on 7 December 1972.