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science.facts.pep.zone

~≈♥Mountains♥≈~

A mountain is a steep-sided mass of rock, rising at least 2,000 ft (600 m) above sea level. Mountains are found on land and under the sea. Some are isolated peaks, but most are found ina RANGE .
HOW ARE MOUNTAINS FORMED?
Mountains are formed by movements of the huge tectonic plates that make up Earth’s crust. Fold mountains are formed when plates collide. Block mountains occur when a slab of land is forced upward.Volcanic mountains are built up from layers of cooled and hardened lava and ash.
ARE MOUNTAINS STILL GROWING?
Some relatively young mountains arestill rising, as colliding plates continue to force the land at their edges upward. At the same time, mountains are constantly eroded by ice, rain, and the wind.
WHY ARE MANY MOUNTAINS SNOW-CAPPED?
Mountaintops are cold because the thin air high up does not hold the Sun’s heat well, and the temperature falls 1.8°F (1°C) for every 500 ft (150 m) of height. It is therefore cold enough to snow over high peaks (even on the equator), and since the temperature rarely rises above freezing, the snow never melts.
MOUNTAINS AT SEA
Some of the world’s tallest mountains lie mostly underwater, with only their summits breaking the surface. Mauna Kea in Hawaii rises 33,480 ft (10,205 m) from the ocean bed, which makes it taller thanMount Everest.
RANGES
Most mountains are found in groups called ranges, such as the Jura Mountains in Europe and the Sierra Nevada Mountains of California. Often, a series of ranges is connected in a larger chain of mountains called a cordillera.
WHERE IS THE WORLD’S LONGEST MOUNTAIN CHAIN?
The longest mountain chain on land is the Andes, which runs for 4,470 miles (7,200 km) down the western edge of South America. An undersea mountain chain called the Mid-Atlantic Ridge is even longer. It stretches 7,000 miles (11,300 km) down the center of the Atlantic Ocean.
Earth’s crust is made of rock, and rock is made of natural substances called MINERALS . There are three main types of rock—sedimentary, igneous, and metamorphic rock. Eachtype is produced in different ways. The oldest rocks on Earth were formed about 3.8 billion years ago.
THE ROCK CYCLE
The rocks that form Earth’s crust are continually destroyed and remade in an endless process called the rock cycle. Rock is formed by melting; by cooling and solidifying; by changing through heat and pressure; by weathering and erosion; and by compression and cementation.
WHAT ARE IGNEOUS ROCKS?
Igneous rocks form when magma (molten rock) rises from deep underground and cools and solidifies at or near Earth’s surface. Igneous rock that forms under the ground may later reach the surface because of geological upheaval. It may also beexposed as the rocks above are wornaway.
Igneous or volcanic rock includes granite and basalt.
WHAT ARE SEDIMENTARY ROCKS MADE OF?
Sedimentary rocks are made of fine rock particles that have been worn away and then carried by rivers, glaciers, or the wind and collect in lakes and oceans. The tiny fragments are then compressed (squashed) and cemented together to form sedimentary rock in a process called lithification.
This rock includes sandstone, limestone, and chalk.
HOW ARE METAMORPHIC ROCKS CREATED?
Metamorphic rocks are formed whenexisting rocks are changed underground by great heat or pressure, or both. When volcanoes erupt and when mountains are formed by the movement of Earth’s tectonic plates, rocks are heated and squeezed. The minerals in the rocks are then changed, forming metamorphic rocks.
Metamorphic rock includes marble, slate, and schist.
MINERALS
Rocks are made of natural, nonliving chemical substances called minerals. Some rocks contain only one mineral.For example, marble is made of the white mineral calcite. Most rocks, however, contain CRYSTALS of severaldifferent minerals.
WHAT ARE THE MOST VALUABLE MINERALS?
Some of the most valuable minerals are ores— minerals that contain metals such as gold, iron, and aluminum. Of these, gold is the most precious because it is soft and easy towork and does not tarnish. Other minerals are prized as GEMSTONES . Fossil fuels, such as coal, produce energy. Minerals such as sulfur and mica are used in industry. Granite and sandstone are used as building stones.
CRYSTALS
Crystals are solid, regular, geometric shapes formed by most minerals. They have smooth surfaces (called faces), straight edges, and symmetrical corners because they are built up from a regular framework of atoms (tiny particles) called a lattice.
HOW DO CRYSTALS FORM?
Crystals form as a molten solid (such as molten rock) cools, or as liquid evaporates (turns into water vapor) from a solution that contains a dissolved mineral. A crystal grows as more and more atoms attach to the basic lattice. Slow-growing crystals are larger than those that form quickly.
These purple crystals are a type of quartz. They formed in hot water, rich in the mineral silica.
GEMSTONES
About 50 of the 3,000 minerals foundon Earth are prized as gemstones. Although they may not shine in their natural state, they can be cut and polished to form sparkling stones. Diamonds, the hardest minerals on Earth, are made of pure, crystallized carbon and are among the world’s most prized gemstones.
WHERE ARE GEMSTONES FOUND?
Many gemstones are found in mountainous regions, usually in rocks that have been subjected to great heat or pressure. They are also found in the sediment on lake and river beds. Diamonds are often mined from rocks found deep underground.
Rubies are made of a mineral called corundum. Rare, deep-red rubies are precious stones, as are diamonds andemeralds.


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