Hexahedrites are one of three broad categories of iron meteorite (the others are octahedrites and ataxites). Hexahedrites are uncommon irons dominated by kamacite, an iron-rich Fe-Ni metal alloy. The common variety of iron meteorite, the octahedrite, is dominated by both kamacite and taenite (a nickel-rich Fe-Ni metal alloy). Hexahedrites are samples from the core of a differentiated asteroid/dwarf planet.
The two photos below are the front & back of a cut, polished, and nitric acid-etched slice of hexahedrite. Unlike octahedrites, hexahedrites lack WidmanstŠtten structure. Almost all the metal you're seeing is kamacite (~5.4 weight-percent nickel here). The variously oriented sets of fine lines are Neumann lines, representing shock twinning planes of kamacite. The blackish-colored needles and small patches are called rhabdites. These rhabdites are composed of the mineral schreibersite, an iron-nickel-cobalt phosphide - (Fe,Ni,Co)3P.
Hexahedrite cut & polished & nitric acid-etched slice (1.7 cm across). The silver metal is kamacite; the dark needles & small patches are schreibersite.
This hexahedrite sample from the Richland (Fredericksburg) Meteorite of Texas, USA. The Richland Meteorite was found in Navarro County, east-central Texas. The Fredericksburg Meteorite apparently was found in Gillespie County, central Texas. Chemical analysis has demonstrated that they are identical.
Hexahedrite cut & polished & nitric acid-etched slice (flip side of above specimen, 1.7 cm across).
Hexahedrite cut & polished & nitric-acid etched slice (1.7 cm across). If anyone knows what these scattered small shiny grains are (taenite? tetrataenite? antitaenite?) that show up under low-angle illumination, let me know.