Weird and Wonderful of Nature: Rock Types and Formations

Weird and Wonderful of Nature: Rock Types and Formations

By Mr Ghaz, December 2, 2011

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Rock Types and Formations around the World

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Core Facts

Rocks are created b heat and pressure within Earth’s crust. Over time, rock alters its form, with old rock being recycled into new,

The three main types of rock are sedimentary, igneous and metamorphic.

Igneous rock makes up most of the part of the planet, partially covered with thin layers of sedimentary and metamorphic rock.

Rocks provide an almost unlimited source of materials for buildings, roads and a range of industrial processes.

Continuous Production

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Igneous rock forms when molten rock, or magma, migrates up to the crust, where it cools and solidifies. Common igneous rocks include peridotite, basalt, gabbro, dolorite and granite. Metals such as gold, silver and copper form around igneous granite.

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Igneous rocks exposed at the surface undergo weathering and erosion, which produces sediment. This is eventually carried out to sea, where it collects in layers. These become increasingly deeply buried and compressed by the weight of over lying layers to form sedimentary rock. Examples include sandstone, limestone, chalk and shale. Sedimentary rock is the principal source of coal, oil and gas, and metals such as iron and aluminum. It provides cement and other natural building materials. Most of the underground fresh water on the planet is stored in it. Some sedimentary rock contains the fossil remains of past life. Also, because sedimentary rock is made up of the remains of earlier rock, it provides clues to the Earth’s biological history.

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Metamorphic rock is produced from pre-existing rock that is altered, but not melted, by heat and pressure deep blow the Earth’s surface. Common metamorphic rocks include marble, which forms from limestone, and slate from shale or mudstone. If the pressure and heat increase to the point where the rock melts, magma forms to produce new igneous rock.

Skeletal Rock

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Limestone represents 10 per cent of all sedimentary rock. Most limestone forms in marine environments from the fossilized remains, of the shells and skeletons of tiny organisms, which rain down on the ocean floor and gradually become compacted into layers of sediment.

There are two types of limestone in which its biological origins are very obvious: coquina, a coarse rock composed of poorly cemented shell fragments; and chalk, a porous, soft rock consisting almost entirely of the shells and skeletons of marine creatures.

Basalt Pillars

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Basalt is particularly hot, fluid lava that spreads easily and can cover large areas. As the lava slowly cools its contracts and cracks in a regular five or seven-sided pattern. The cracks extend from top to bottom of the rock, resulting in a network or pillars or column with very thin gaps between them. The Giant’s Causeway on the Antrim coast of Northern Ireland and Figal’s Cave on the Hebridean island of Staffa are good examples.

Organs Pipes: Straight-sided columns are clearly visible in these basalt pillars at Sawn Rocks, Australia.

Weird and Wonderful

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The Rock of Gibraltar is the remnant of natural dam that cut off the Mediterranean from the Atlantic around 8 million years ago as the African and Eurasian plates collided and forced the seafloor upwards.

Common Uses of Different Rocks

Granite: Resistant to weathering. Often at core of eroded mountains. Building material, paving, tombstones.

Pumice: Volcanic origin and glassy texture. An abrasive in cleaning, polishing and scouring; an aggregate in masonry, concrete, insulation and acoustic tiles.

Chalk: Varied uses in fertilizer, cement, putty, as whiting in cosmetic (but not school chalk).

Clay: Used in tiles, bricks, ceramics, sculpture, paper coating, water softener, Portland cement.

Conglomerate: Made up off gravels. Used for construction and in road- building.

Flint: Used in building, road constructions, sandpaper, as a grinding agent and in concrete aggregate.

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Limestone: Used in flooring, Portland cement, fertilizer. An ingredient in steel and glass.

Sandstone: Varieties include quartz, sandstone, arkose and greywacke. Used as a building material.

Shale: Most common sedimentary rock. Crumbles easily. Ingredient in tiles, bricks, pottery, ceramics, cement.

Slate: Breaks into flat slabs. Used for electrical panels, tabletops (snooker, laboratories), blackboards, roofing and flooring.

Marble: Relatively soft and easy to cut and shape. Used for building, flooring, sculpture, tabletops.