Plutonic Rocks Phaneritic texture is sometimes referred to as coarse-grained igneous texture. Granite, the most well known example of an intrusive igneous rock, has a phaneritic texture.

Igneous rocks form when magma (molten rock) cools and crystallizes, either at volcanoes on the surface of the Earth or while the melted rock is still inside the crust. All magma develops underground, in the lower crust or upper mantle, because of the intense heat there.

Characteristics of Igneous Rocks Most igneous forms include more than one mineral deposit. They can be either glassy or coarse. These usually do not react with acids. The mineral deposits are available in the form of patches with different sizes.

Igneous rocks are formed from melted rock deep inside the Earth. Sedimentary rocks are formed from layers of sand, silt, dead plants, and animal skeletons. Metamorphic rocks formed from other rocks that are changed by heat and pressure underground.

Igneous Rock Classification

Rocks formed by the evaporation of water are called evaporites – gypsum, anhydrite, halite (common salt). This evaporation may occur in either shallow basins on land or in the sea. Material (salts) is eroded from land surfaces and is then carried to the sea by rivers.

The origin of fine-grained igneous rock is magma, or molten rock that erupts from a volcano in the form of lava.

• Rock.
• Granite.
• Pumice.
• Felsic and mafic rocks.
• Basalt.
• Perlite.
• obsidian.
• Trachyte.

Igneous rocks are formed in molten magma….Igneous Rock Image courtesy of Antpkr/ Free Digital Photos

• ‘Igneous’ comes from the latin phrase ‘made from fire’.
• Earth’s moon is made out of igneous rocks.
• Many roads are made from crushed igneous rock .
• The igneous rock called pumice is the lightest rock on earth.

Igneous rocks are also very important because their mineral and chemical makeup can be used to learn about the composition, temperature and pressure that exists within the Earth’s mantle. They can also tell us much about the tectonic environment, given that they are closely linked to the convection of tectonic plates.

Rocks and minerals are all around us! They help us to develop new technologies and are used in our everyday lives. Our use of rocks and minerals includes as building material, cosmetics, cars, roads, and appliances. Rocks and minerals are important for learning about earth materials, structure, and systems.

basalt

Basalt

Some examples of metamorphic rocks are gneiss, slate, marble, schist, and quartzite. Slate and quartzite tiles are used in building construction. Marble is also prized for building construction and as a medium for sculpture.

Sedimentary rocks

Examples of extrusive igneous rocks are basalt, andesite, rhyolite, dacite, obsidian, pumice and scoria. Komatiite, a rare extrusive igneous rock, required much hotter melting temperatures to form than occur now.

In 1999, the oldest known rock on Earth was dated to 4.031 ±0.003 billion years, and is part of the Acasta Gneiss of the Slave craton in northwestern Canada.

Scientists analysing a meteorite have discovered the oldest material known to exist on Earth. They found dust grains within the space rock – which fell to Earth in the 1960s – that are as much as 7.5 billion years old.