What is the meaning of petrography & petrogenesis?
Petra is the Greek for rock. Petrology is the science of rocks; petrography and petrogenesis are subdisciplines: petrography is concerned with the description of rocks; petrogenesis with the ways in which they are formed. Three major divisions of rocks are recognized in geology: igneous, metamorphic, and sedimentary. Each of these terms carries petrogenetic connotations. Igneous rocks are those that have formed from molten magma. Metamorphic rocks, as the name implies, are those that have formed by the modification in the solid of an existing rock by the effects of heat and pressure. Most sedimentary rocks are formed at the surface of the Earth by deposition of particles that have been eroded or weathered from pre-existing rocks, which can be igneous, metamorphic, or sedimentary. Some sedimentary rocks are formed of particles deposited by or from a fluid by chemical or biological precipitation. There are some rocks where more than one set of processes has been active in their formation
