Slide2:
Did an Impact Make the Mysterious Microscopic Magnetite Crystals in ALH 84001? ALH 84001 is an old rock that crystallized in a large body of magma deep in the Martian crust 4.5 billion years ago.
An impact event excavated the rock to a location near the surface, where water evaporated and precipitated carbonate minerals, including iron carbonate (siderite), along grain boundaries.
The rock was shocked after that event, causing assorted deformation of the carbonates, possibly including decomposition of the siderite. A Brief Geologic History of Martian Meteorite ALH 84001
Slide3:
Did an Impact Make the Mysterious Microscopic Magnetite Crystals in ALH 84001? Mary Sue Bell’s laboratory experiments show shock decomposition of siderite and its transformation to magnetite when shocked to 49 GPa.
Magnetite crystals produced in Bell’s shock experiments have the same size range, composition, and shapes as some of the magnetites found in ALH 84001.
The tiny crystals of magnetite in ALH 84001 might have been made when shock waves decomposed iron carbonate, as during an impact event.
This transmission electron microscope image shows the transformation of siderite to magnetite when shocked to 49 GPa pressure in the lab. In the upper right area, labeled "S", is siderite containing nucleating crystals of magnetite. The other crystals in this image, labeled “a,b,c” are magnetites of different shapes.