I-types are important because they can readily be recovered from sedimentary rocks allowing study of solar system events over geological time. We report the results of a study of the mineralogy and petrology of 88 I-type cosmic spherules recovered from Antarctica in order to evaluate how they formed and evolved during atmospheric entry, to constrain the nature of their precursors and to establish rigorous criteria by which they may be conclusively identified within sediments and sedimentary rocks. Two earth materials introduction to mineralogy and petrology pdf of OX spherule are distinguished, magnetite-poor dendritic spherules and magnetite-rich coarse spherules.
Six OXMET particles having features of both MET and OX spherules were also observed. Precursors are suggested to be mainly kamacite and rare taenite grains. 100 and suggest that metal from H-group ordinary, CM, CR and iron meteorites may form the majority of particles. OX spherules owing to differences in particle size, entry angle and velocity. Magnetite-poor OX spherules are shown to form by crystallisation of non-stoichiometric wüstite at the liquidus followed by sub-solidus decomposition to magnetite, whilst in magnetite-rich OX spherules magnetite crystallises directly at the liquidus. Magnetite rims found on most particles are suggested to form by oxidation during sub-solidus flight. Non-equilibrium effects in the exchange of Ni between wüstite and metal, and magnetite and wüstite are suggested as proxies for the rate of oxidation and cooling rate respectively.
Variations in magnetite and wüstite crystal sizes are also suggested to relate to cooling rate allowing relative entry angle of particles to be evaluated. The formation of secondary metal in the form of sub-micron Ni-rich or Pt-group nuggets and as symplectite with magnetite was also identified and suggested to occur largely due to the exsolution of metallic alloys during decomposition of non-stoichiometric wüstite. Weathering is restricted to replacement of metal by iron hydroxides. Petrology has three subdivisions: igneous, metamorphic, and sedimentary petrology.
The work of experimental petrologists has laid a foundation on which modern understanding of igneous and metamorphic processes has been built. This page was last edited on 22 January 2018, at 08:50. Specific studies within mineralogy include the processes of mineral origin and formation, classification of minerals, their geographical distribution, as well as their utilization. 1837, and in a later edition introduced a chemical classification that is still the standard. An initial step in identifying a mineral is to examine its physical properties, many of which can be measured on a hand sample. A harder mineral will scratch a softer, so an unknown mineral can be placed in this scale by which minerals it scratches and which scratch it.
The crystal structure is the arrangement of atoms in a crystal. The lattice can be characterized by its symmetries and by the dimensions of the unit cell. There are 32 possible crystal classes. X-rays have wavelengths that are the same order of magnitude as the distances between atoms. In a sample that is ground to a powder, the X-rays sample a random distribution of all crystal orientations. Since 1960, most chemistry analysis is done using instruments.
The solution is vaporized and its absorption spectrum is measured in the visible and ultraviolet range. In addition to macroscopic properties such as color or lustre, minerals have properties that require a polarizing microscope to observe. Light passes successively through the polarizer, the sample and the analyzer. If there is no sample, the analyzer blocks all the light from the polarizer.
However, an anisotropic sample will generally change the polarization so some of the light can pass through. Thin sections and powders can be used as samples. When an isotropic crystal is viewed, it appears dark because it does not change the polarization of the light. Systematic mineralogy is the identification and classification of minerals by their properties.