Rocks and Volcanoes

 Physical Feature is a term used to describe the structure and formation of land. Physical Features are often named because of their height, shape or what they are made of. Some examples of Physical Features are mountains, rivers, rocks and volcanoes.

 Igneous rock may form with or without crystallization, either below the surface as intrusive rocks or on the surface extrusive rocks while sedimentary rocks are formed by the deposition of material at the Earths’ surface and within bodies of water.  Igneous rocks are formed from molten liquid minerals called magma, while sedimentary rocks are formed from cementing, compacting and hardening of existing rocks.  Igneous rocks are non porous for water, while sedimentary rocks porous to the water. This means that water cannot penetrate through igneous rocks but can penetrate through sedimentary rocks.  Igneous rocks are harder than sedimentary rocks.  Sedimentary rocks react higher to acid compared to igneous rocks.  Igneous rocks can be light or dark colored, while sedimentary rocks have a variety of colors.

 The four (4) major groups of Igneous Rocks are:

 Basalt- is a dark colored, fine-grained, igneous rock composed mainly of plagioclase and pyroxene minerals. It most commonly forms as an extrusive rock, such as a lava flow but can also form in small intrusive, bodies such as an igneous dike.

 Andesite- is an extrusive rock intermediate in composition between rhyolite and basalt. Andesite lava is of moderate viscosity and forms thick lava flows and domes.

 Dacite- is a volcanic rock that may be considered a quartz-bearing variety of andesite. Dacite is primarily associated with andesite and trachyte and forms lava flows, dikes and sometimes massive intrusions in centers of volcanoes.

 Rhyolite- is an extrusive rock with a very high silica content. It is usually pink or gray in color with grains so small that they are difficult to observe without a hand lens.

 The four (4) major types of volcanoes are:

 Cinder Cones- are the simplest type of volcano. They are built from particles and blobs of congealed have ejected from a single vent. As the gas-charged lava is blown violently into the air, it breaks into small fragments that sodify and falls as cinders around the vent to form a circular or oval cone.

 Composite Volcano- a strato-volocano also known as a composite volcano is a conical volcano built up by many layers of hardened lava, tephra, pumice and volcano ash.

 Shield Volcanoes- is a type of volcano usually built almost entirely of fluid lava flows. They are named for their low profile, resembling a warrior’s shield lying on the ground.

 Lava Volcano- is the structured typically formed when lava emerges from an underwater volcanic vent or sub-glacial volcano or a lava flow enters the ocean.

Done By: Vidaijah Richardson Saunjae Connor Mariella Webster Lo’Marah Harrigan