Bradley J P, Harvey R P, McSween H Y
MVA Inc., Norcross, GA 30093, USA.
Geochim Cosmochim Acta. 1996;60(24):5149-55. doi: 10.1016/s0016-7037(96)00383-3.
Nanometer-sized magnetite crystals associated with carbonates in fracture zones within Martian meteorite ALH84001 have been examined using analytical transmission electron microscopy. Some of the crystals exhibit distinctive morphologies: filamentary rods and ribbon, and platelets. The rods and ribbons are elongated along the crystallographic [100] and [111] directions. Some of the rods contain microstructural defects indicating that they grew by spiral growth about screw dislocations. Platelets are flattened along the [100] and [110] directions. These unique morphologies and microstructures constrain the growth conditions of magnetite. The whiskers and platelets most likely formed in the temperature range 500-800 degrees C by direct condensation from a vapor or precipitation from a supercritical fluid, and their properties are inconsistent with a biogenic origin.
利用分析透射电子显微镜对火星陨石ALH84001断裂带中与碳酸盐相关的纳米级磁铁矿晶体进行了研究。部分晶体呈现出独特的形态：丝状棒体、带状以及片状。棒体和带状晶体沿晶体学[100]和[111]方向拉长。部分棒体含有微观结构缺陷，这表明它们是围绕螺旋位错通过螺旋生长而形成的。片状晶体沿[100]和[110]方向扁平。这些独特的形态和微观结构限制了磁铁矿的生长条件。晶须和片状晶体很可能是在500 - 800摄氏度的温度范围内，通过蒸汽直接冷凝或超临界流体沉淀形成的，其性质与生物起源不一致。
