Petrography in the context of "Electron microprobe"

A stratigraphic unit is a volume of rock of identifiable origin and relative age range that is defined by the distinctive and dominant, easily mapped and recognizable petrographic, lithologic or paleontologic features (facies) that characterize it.

Units must be mappable and distinct from one another, but the contact need not be particularly distinct. For instance, a unit may be defined by terms such as "when the sandstone component exceeds 75%".

A petrographic microscope is a type of optical microscope used to identify rocks and minerals in thin sections. The microscope is used in optical mineralogy and petrography, a branch of petrology which focuses on detailed descriptions of rocks. The method includes aspects of polarized light microscopy (PLM).

In optical mineralogy and petrography, a thin section (or petrographic thin section) is a thin slice of a rock or mineral sample, prepared in a laboratory, for use with a polarizing petrographic microscope, electron microscope and electron microprobe. A thin sliver of rock is cut from the sample with a diamond saw and ground optically flat. It is then mounted on a glass slide and then ground smooth using progressively finer abrasive grit until the sample is only 30 μm thick. The method uses the Michel-Lévy interference colour chart to determine thickness, typically using quartz as the thickness gauge because it is one of the most abundant minerals.

When placed between two polarizing filters set at right angles to each other, the optical properties of the minerals in the thin section alter the colour and intensity of the light as seen by the viewer. As different minerals have different optical properties, most rock-forming minerals can be easily identified. Plagioclase for example can be seen in the photo on the right as a clear mineral with multiple parallel twinning planes. The large blue-green minerals are clinopyroxene with some exsolution of orthopyroxene.

In the archaeology of the Stone Age, an industry or technocomplex is a typological classification of stone tools.

An industry consists of a number of lithic assemblages, typically including a range of different types of tools, that are grouped together on the basis of shared technological or morphological characteristics. For example, the Acheulean industry includes hand-axes, cleavers, scrapers and other tools with different forms, but which were all manufactured by the symmetrical reduction of a bifacial core producing large flakes. Industries are usually named after a type site where these characteristics were first observed (e.g. the Mousterian industry is named after the site of Le Moustier). By contrast, Neolithic axeheads from the Langdale axe industry were recognised as a type well before the centre at Great Langdale was identified by finds of debitage and other remains of the production, and confirmed by petrography (geological analysis). The stone was quarried and rough axe heads were produced there, to be more finely worked and polished elsewhere.

Igneous petrology is the study of igneous rocks—those that are formed from magma. As a branch of geology, igneous petrology is closely related to volcanology, tectonophysics, and petrology in general. The modern study of igneous rocks uses a number of techniques, some of them developed in the fields of chemistry, physics, or other earth sciences. Petrography, crystallography, and isotopic studies are common methods used in igneous petrology.