The Rocks: Formation and Types
An essential and important part of Earth Science is geology. Geology is
the science that studies the dynamics and physical history of Earth, the rocks
of which is it composed and chemical, biological and physical changes that
occur on Earth. As is established in the definition, geology studies the
composition of Earth, mainly, the rocks. The rocks are aggregates of solid
minerals of natural origin, whose components are defined and are arranged
inside forming crystals. The Earth is a rocky planet, this mean that most of
its mass is in the form of rocks. Therefore, we can study the types, formation
and changes of the rocks in a general form.
First, we need to know the types and formation of the rocks that exist
over the Earth’s surface. In Earth there are three kinds or rocks: Igneous,
Sedimentary and Metamorphic. The same can be classified by their origin,
formation, composition and their changes.
Igneous rocks are formed by the cooling the molten rock product of
volcanic activity. These rocks are classified into two main subgroups:
extrusive igneous or volcanic and intrusive igneous or plutonic. Volcanic rocks
consists of fine crystals formed by rapid cooling of lava near the Earth’s
surface; some of these rocks are rhyolite, andesite, basalt, scoria, pumice and
some pyroclastic rocks (formed by pieces of rocks that have been thrown into
the air by volcanic explosion) like gaps,
tuffs, volcanic conglomerates and basaltic flows. On the other hand, the
plutonic rocks are composed of thick crystals formed by the slow cooling of the
magma inside the Earth’s surface; some of these rocks are granite,
granodiorite, diorite, gabbro and periodite. These rocks are exposed to Earth’s
surface by erosion and weathering processes.
Sedimentary rocks are formed when sediments or fragments are compacted
and cemented, also it accumulates layers upon layers through the years. These
rocks are classified onto three main subgroups: clastic, non-clastic and
bioclastic. Clastic sedimentary rocks are formed by pieces of other rocks.
Example of this are conglomerates, gaps, sandstone, limonite, argillaceous
slate. Non-clastic sedimentary rocks are these formed by materials that have
precipitated directly from water, rocks like dolomite, flint, halite (salt
rock) and gypsum rock are samples of these types of rocks. Bioclastic
sedimentary rocks are originated by the accumulation of skeletons of sea
plants, animals and coral reef that have died. Limestone is a bioclastic
sedimentary rock formed by calcium carbonated and calcite; hard coal, composed
by vegetal materials is also a type of these rocks.
Finally, we have the metamorphic rocks that are formed by changes in
temperature and pressure of the rock and other chemical processes. These rocks
can be formed from other metamorphic rocks, sedimentary or igneous. There exist
two types of metamorphism: contact metamorphism and regional metamorphism.
Contact metamorphism is produced when igneous rocks and lava flows remains
trapped between the layers of other rocks, these are classified as not foliated
rocks (rocks without sheets), are formed by chemical reactions, high pressure
and temperatures, are subdivided by grain size; marble (originated from
limestone and calcite compound) and quartzite (originated from quartzarenite
and quartz compound) are not foliated rocks of thick grains; serpentine (a
slippery blue-green rock originated from olivine and basalt rocks and quartz
and amphibole composed) is a not foliated rock of fine grains. Regional
metamorphism is formed more slowly that the contact metamorphism and it
includes large regions and it has a deeper metamorphic rock zone, are formed by
big pressure and high temperatures, these are classified as foliated rocks
(rocks with sheets); schist (originated from phyllite and mica composed) and
gneiss (originated from granite or volcanic rocks and composed of different
minerals) are foliated rocks of thick grains; phyllite (originated from
argillaceous slate and mica, quartz and chlorite composed) and slate
(originated from argillaceous slate and mica, quartz, clay and chlorite
composed) are foliated rocks of fine grains.
For humans beings the study of rocks is very important. Many monuments,
sculptures and buildings are made from different types of rocks. They are also used
by sculptors to make buildings and artistic works such as marble. For example
cemetery tombstones are made from granite and basalt rocks. The statues are
made from sedimentary rocks, specifically limestone rocks. These and other
economic uses are indispensable for constructions made by humans over time.
References:
Information:
Serie Naturales.
(1998). Descubrimiento 9 Ciencia Integrada.
Puerto Rico:
Ediciones
Santillana, Inc.
Curso General de Suelos
(AGRO 3005). Laboratorio #3: Rocas y minerales
Picture:
No hay comentarios.:
Publicar un comentario