World Book Trivia Challenge Advanced--4/9-rocks

Several processes can create metamorphic rock. In contact metamorphism, heat produced by nearby magma (molten igneous rock) causes recrystallization. In regional metamorphism, both heat and pressure change rock. Pressure comes from the burial of the rocks deep in Earth's crust. Movements in the crust may also affect the rock by deforming it. These movements are often associated with the formation of mountains. In a less common process, dynamic metamorphism, only deformation due to crustal movements alters rock. In hydrothermal metamorphism, hot water provides heat that changes the rock. The water often also reacts with the rock, causing chemical changes.

Climbing, also called rock climbing, is the sport of ascending steep rock surfaces. The sport developed during the 1800's from mountain climbing. Rock climbing close to the ground is called bouldering.

Most rocks are aggregates. Aggregates contain crystals or grains of two or more different minerals. Much granite, for example, contains grains of clear quartz, pinkish potassium feldspar, white plagioclase, and black biotite or hornblende. Some rocks have grains so small that they can be seen only when a thin slice of the rock is examined under a microscope.

Igneous rock forms from magma (molten rock). Magma is extremely hot, with temperatures ranging from 1400 to 2300 °F (760 to 1300 °C). Most magma lies deep below Earth's surface. Sometimes, magma rises to the surface through fissures (deep cracks) in Earth's crust.

Zuma Rock is a symbol of Nigeria and a popular tourist destination. The rock appears on Nigeria’s 100-naira bill.

Such metals as aluminum, copper, iron, lead, tin, and zinc come from rocks called ores. Ores also supply radioactive metals, such as uranium, and nonmetallic minerals, such as borax, graphite, and trona. In Minnesota and western Australia, deposits of iron ore make up entire mountains. In tropical climates, weathering (the wearing away of rock) creates thick soils rich in the aluminum-bearing ore bauxite

The continent of Australia has rocks that rank among the oldest in the world. Some of them formed over 3 billion years ago. A great variety of rocks of all ages can be found throughout Australia.

Each type of rock develops from other types of rock. To help explain how rocks form, geologists sometimes refer to a series of transformations called the rock cycle. The rock cycle begins with igneous rock created by magma flowing to Earth's surface. Weathering alters the rock chemically and breaks it into particles. The particles accumulate and harden to form sedimentary rock. As the sedimentary rock becomes buried, heat and pressure transform it into metamorphic rock. With enough heating, metamorphic rocks melt into magma that can form igneous rock, completing the cycle.
Rock rarely proceeds through the entire rock cycle. The cycle may be halted, or steps can be skipped, repeated, or reversed. For example, some igneous rocks transform directly into metamorphic rock, and sedimentary rock can weather and then lithify to form other kinds of sedimentary rock.

Shale is a fine-grained sedimentary rock that is formed by the compression of muds. This type of rock is composed primarily of quartz and minerals that are found in clay. Shales can be broken easily into thin, parallel layers. Shale is ground up for use in making bricks and cement.

Petrology is a branch of geology that deals with the origin and composition of rocks. Petrologists analyze the physical and chemical conditions involved in the formation of the three major types of rocks: igneous, metamorphic, and sedimentary. Such analysis helps provide clues to the origin and development of the earth.