Nanometer-sized mineral grains and their genetic types in meteorites

Three genetically different types of nanometer-sized mineral grains in meteorites can be distinguished based on literature and original data: (a) primitive condensates, (b) metamorphic grains, and (c) weathering products. The first of these groups were formed by condensation in a gas-dust nebula in either a presolar or solar environment. Metamorphic grains were formed as a result of thermal, shock or aqueous metamorphism on the meteorite parent bodies. The third type can clearly be characterized as terrestrial weathering products, which are generally found in meteorite finds and are rare or absent within meteorites recovered shortly after having fallen. Nanometric components are found predominantly within the fine-grained silicate material of primitive meteorites. It is suggested that enhanced accretional properties of nanometer-sized grains could be responsible for the primary accretion of condensed nanoglobules within a protoplanetary nebula. The nature of nanometer-sized inclusions of native W and native Ag originally discovered in the Krymka chondrite is preliminarily discussed