NWA 6953, Ancient Crystallized Mesosiderite, Micromount



Northwest Africa 6953 is an interesting mesosiderite whose unique nature is a result of its composition and the collective effects of long-term terrestrial weathering. The metal content in NWA 6953 has experienced dramatic alteration and has almost entirely been replaced with the iron oxyhydroxide goethite. But it’s not the oxidation or alteration alone that makes this meteorite fascinating. Studying how the iron oxidation process takes place on Earth in NWA 6953, a predominantly orthopyroxene-rich meteorite, may have huge implications for comparing how iron oxidation may take place in aqueous environments on other alien worlds. More importantly, studying this meteorite can potentially reveal clues as what to look for in discovering other highly terrestrialized meteorites that until now have mostly gone unnoticed.

This meteorite fell 40-50 thousand years ago when the Saharan desert was sub-tropical. It was not a desert then, and the area experienced rainfall much like any other place on Earth. NWA 6953 was exposed to a much wetter environment, and after many millennia of weathering (at the surface and even during burial and exhumation) nearly all the metal has been replaced with terrestrial minerals. In fact, the visual appearance of the meteorite has been radically changed into a strange and beautiful form that is unlike any other in terms of aesthetics and chemistry. Voids in the meteorite matrix have been filled with terrestrial minerals in crystal form, producing a prismatic effect with internal reflections.

The visual similarities of this meteorite to a weathered orthopyroxenitic diogenite gives some casual credence to the theory that asteroid 4 Vesta may be the parent body of mesosiderites, and when the classification results came back as a mesosiderite, everyone involved was quite surprised. The original metal content (estimated to be about 30-40% by volume) has been replaced by carbonates and goethite. However, the original orthopyroxene, calcic plagioclase, minor olivine and some troilite remain, and even a few rare grains of the original taenite and kamacite have survived. The refractive quality of the crystal mixture is amazing, and another quality of this meteorite is the presence of water trapped within the matrix during the terrestrialization of iron hydroxides. 

Refer to the photo. The black centimeter cube is shown for scale and is not included. You are purchasing a small fragment selected from the larger lot shown. Your purchase will include a labeled gemjar for safe storage.