Sat, September 30, 2017 at 12:55 pm GMT
hi today i want to share with you about Rocks
ROCKS
A rock is an aggregate of mineral particles found in soft, solid or unconsolidated state. The earth‘s crust consists of rocks and rocks consist of a combination of different minerals. All minerals are formed from one or more of eight main elements. These are: oxygen, silicon, potassium, sodium, calcium, magnesium, iron and aluminum.
Rocks can be broadly categorized into three types. These are igneous rocks, sedimentary rocks and metamorphic rocks. These kinds of rocks are classified according to their origin, chemical composition and age.
The Characteristics of the Earth's Crust, the Mantle and the Core
Describe the characteristics of the earth's crust, the mantle and the core
Variations in characteristics of the three interior zones of the earth are the result of temperature and pressure as they increases from the surface to the center of the earth. Factors which accounts for such variations includes: pressure on the underlying materials, weight of the underlying materials, radioactivity, magma movement and heat generated during the formation of the earth.
The Types of Rocks of the Earth's Crust
Identify types of rocks of the earth's crust
Igneous rocks
These rocks are formed when molten rock cools and solidifies. All igneous rocks originate inside the earth where they are under great pressure. Igneous rocks do not occur in layers and they don‘t contain fossils which are the chemically-changed remains of ancient plants and animals embedded in rocks. These rocks solidify either within the earth‘s crust and form intrusive features or outside the earth‘s surface and form extrusive features.
Igneous rocks are formed when the molten magma is forced out from the upper mantle to the earth‘s surface, where it cools and solidifies due to low temperature. Crystals form on cooling and the rocks are called crystalline rocks.
There are two main types of igneous rocks:
1. Plutonic: these have solidified deep in the crust and they are seen on the surface only after being exposed by prolonged erosion.
2. Volcanic: these have been poured on the earth‘s surface where they are called lavas.
Characteristics of igneous rocks
Igneous rocks reflect light.
They are not found in layers.
They do not contain fossils.
They are crystalline rocks.
They are formed through cooling and solidification of magma.
They can undergo metamorphic and weathering processes.
They contain different minerals like iron, magnesium etc.
Many igneous rocks are found in Dodoma, Iringa and in the shores of Lake Victoria (Mwanza). The main examples are granite, gabbro, basalt and diorite. Some are found in Kilimanjaro and Rungwe (Mbeya) such as basalt, pumice, diorite, gabbro, syenite and peridotite rocks.
Granite
Basalt rocks
Sedimentary rocks
Sedimentary rocks are found in layers; they contain fossils and are very soft. These are weathered particles formed through deposition and lithification processes. Sedimentary rocks are formed when the sediments are accumulated, compacted and cemented together. The sediments are compacted by compression to form sedimentary rocks. These are called stratified rocks.
Characteristics of sedimentary rocks
They are formed when particles or sediments are accumulated, compacted and cemented together.
They contain fossils.
They are found in layers (strata).
They do not reflect light.
They are non-crystalline rocks.
They can undergo metamorphic process.
Types of sedimentary rocks
Mechanically-formed sedimentary rocks
These are formed through weathering process. When weathering agents erode and deposit rock particles, they are accumulated, compacted and cemented together to form sedimentary rocks. Examples of mechanically formed sedimentary rocks are clays, gravels and alluviums (all deposited by water), moraines, boulder clay and gravels (deposited by ice) and loess (deposited by wind); sandstones and shale.
Sandstone
Shale: Shale occurs in a wide range of colours that include: red, brown, green, grey, and black.
Chemically-formed sedimentary rocks
These are formed through chemical precipitation process. They include carbonate (as it is in stalactite and stalagmite), sulphate, chloride, etc. The main examples are gypsum, rock salt, lignite, dolomite, flint, borax, limonite, haematite, etc.
Dolomite
Organically-formed sedimentary rocks
These are formed through mineralization process of decaying and decomposition of dead organisms such as animals and plants. The remains of living organisms are accumulated, compacted and cemented together to form these sedimentary rocks. The main examples are chalk (limestone) and coral (formed from animals), and peat, coal and lignite (formed from plants).
Lignite rocks
Limestone
Chalk
Coal
Coral rocks
Metamorphic rocks
These are rocks which have changed their shape, size, appearance or chemical composition due to the contact of heat, pressure or both. This process is referred to as metamorphism. Any rock
