Petrology is a field of geology which focuses on the study of rocks and the conditions by which they form. There are three branches of petrology, corresponding to the three types of rocks: igneous, metamorphic, and sedimentary. The word petrology itself comes from the Greek "petros", or rock.
Igneous petrology focuses on the genesis of rocks that crystallized from a magma.
Metamorphic petrology focuses on the changes that a rock undergoes as a result primarily of extreme pressure and temperature.
Sedimentary petrology focuses on the processes by which sediments, or clastics, are cemented together to form sedimentary rocks.
Petrology utilizes the classical fields of mineralogy, microscopic petrography, and chemical analyses to describe the composition and texture of rocks. Modern petrologists also include the principles of geochemistry and geophysics through the studies of geochemical trends and cycles and the use of thermodynamic data and experiments to better understand the origins of rocks.
Determination of Martian meteorite lithologies and mineralogies using vibrational spectroscopy
The spectra of these meteorites are significantly different from each other, and we can distinguish the three lithologies easily on the basis of their spectral morphologies.
Using a linear deconvolution model, the modal mineralogies of ALH7705, Nakhla, and Zagami were derived from their spectra to within 2–19% of the modes derived by optical methods.
The major lithologies in Unit II are silty clay/claystone with silt and nannofossil clay/claystone (Table 2).
Major lithologies in Subunit IIB are olive-gray, yellowish brown, and moderate brown silty claystone or clayey siltstone, and light greenish, olive gray, and grayish-orange nannofossil or calcareous claystone.
The dominant lithology is serpentinitized peridotite (>90% of all fragments).
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