ROCKS MINERALS The Building Blocks of Earth ROCKS
ROCKS & MINERALS The Building Blocks of Earth
ROCKS VS. MINERALS Rock is an indefinite mixture of naturally occurring substances, mainly minerals. Its composition may vary in containment of minerals and organic substances, and are never exact.
ROCKS VS. MINERALS A mineral is any naturally occurring, inorganic substance, often characterized by an exact crystal structure. Its chemical structure can be exact, or can vary within limits. Elements that occur naturally are also considered minerals.
MINERAL GROUPS All minerals belong to a chemical group: Elements, Sulfides, Oxides, Halides, Carbonates, Nitrates, Borates, Chromates, Sulfates Phosphates, Arsenates, Vanadates, Tungstates, Molybdates, and Silicates.
THREE TYPES OF ROCKS Sedimentary Rocks Igneous Rocks Metamorphic Rock
SEDIMENTARY ROCK For thousands of years, little pieces of our earth have been eroded--broken down and worn away by wind and water. These little bits of our earth are washed downstream where they settle to the bottom of the rivers, lakes, and oceans and deposited in layers on top of each. These layers are pressed down more and more through time, until the bottom layers slowly turn into rock.
CLASTIC ROCKS Sediments may also include pieces of stones and shells and other objects, not just grains of pure minerals. Geologists use the word clasts to denote particles of all these kinds, and rocks made of clasts are called clastic rocks.
MARINE ORGANIC ROCKS Microscopic plankton build shells out of dissolved calcium carbonate or silica. When these plankton die, their bodies accumulate in thick layers on the seafloor. Limestone (carbonate) and chert (silica).
BOTANIC ORGANIC ROCK Dead plant material builds up into thick layers. With a small degree of compaction, this becomes peat and after much longer and deeper burial, it becomes coal.
COAL Although peat is forming in parts of the world today, the great beds of coal we mine formed during past ages in enormous swamps. There are no coal swamps around today, because conditions do not favor them.
CHEMICAL ROCKS As ancient shallow seas began to dry and become more concentrated, minerals begin to precipitate. Calcite (Ca. CO 3), gypsum (Ca. SO 4. 2 H 2 O), and halite (Na. Cl). The resulting rocks are certain limestones or dolomites, gypsum rock, and rock salt respectively. Part of the evaporite sequence.
SEDIMENTARY ROCK Sandstone Limestone Gypsum Conglomerate Shale
SANDSTONE Sandstone rocks are sedimentary rocks made from small grains of the minerals quartz and feldspar. They often form in layers as seen in this picture. They are often used as building stones.
LIMESTONE Limestone rocks are sedimentary rocks that are made from the mineral calcite which came from the beds of evaporated seas and lakes and from sea animal shells. This rock is used in concrete and is an excellent building stone for humid regions.
SHALE Shale rock is a type of sedimentary rock formed from clay that is compacted together by pressure. They are used to make bricks and other material that is fired in a kiln.
CONGLOMERATE Conglomerate rocks made up of large sediments like sand pebbles. The sediment is so large that pressure alone cannot hold the rock together; it is also cemented together with dissolved minerals.
GYPSUM Gypsum rocks are sedimentary rocks made up of sulfate mineral and formed as the result of evaporating sea water in massive prehistoric basins. It is very soft and is used to make Plaster of Paris, casts, molds, and wallboards
METAMORPHIC ROCKS Metamorphic rocks are igneous or sedimentary rocks that have "morphed" into another kind of rock. How do sedimentary and igneous rocks change? The rocks are under tons and tons of pressure, which fosters heat build up, and this causes them to change.
FOUR AGENTS OF METAMORPHOSIS Heat Pressure Fluid Content Strain
METAMORPHIC ROCK Schist Gneiss
SCHIST Schist rocks are metamorphic formed from basalt, shale, or slate, a metamorphic rock. Through tremendous heat and pressure, these rocks were transformed into this new kind of rock.
GNEISS Gneiss rocks are metamorphic that may have been granite, but heat and pressure changed it. The mineral grains in the rock were flattened through tremendous heat and pressure and are arranged in alternating patterns.
IGNEOUS Igneous rocks are formed either underground or above ground from the cooling and crystallization of magma. Extrusive Intrusive Plutonic (aboveground) (below ground) (deep magma)
IGNEOUS MINERALS The main minerals in igneous rocks are: feldspar (silicates) quartz (Si. O 2) olivine (Mg and Fe silicates) mica (sheet silicates)
INTRUSIVE IGNEOUS ROCK Intrusive igneous rocks are formed when magma, becomes trapped in small pockets. As these pockets of magma cool slowly underground, the magma forms igneous rocks. Intrusive rocks cool more slowly (over thousands of years) and have small to medium grains.
DEEP INTRUSIVE IGNEOUS ROCK Igneous rock formed from deep magma is called plutonic. Plutonic rocks cool over millions of years, deep underground, and can have grains as large as pebbles and even a meter across.
EXTRUSIVE IGNEOUS ROCK Igneous rocks are also formed when volcanoes erupt, causing the magma to rise above the earth's surface. When magma appears above the earth, it is called lava. Igneous rocks are formed as the lava cools above ground. Extrusive rocks cool quickly (over periods of seconds to months) and have invisible or very small grains.
IGNEOUS ROCK Granite Scoria Pumice Obsidian
FAMOUS ROCK STARS The two best-known igneous rock types are basalt and granite. Basalt is the dark, fine-grained rock from lava flows and magma intrusions. Its dark minerals are rich in magnesium (Mg) and iron (Fe). Granite is the light, coarse-grained rock formed at depth and exposed after deep erosion. It is rich in feldspar and quartz (silica).
BASALT Basalt is a common extrusive volcanic rock. It is usually gray to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria.
GRANITE Granite rocks are igneous rocks which were formed by slowly cooling pockets of magma that were trapped beneath the earth's surface. Granite is used for long lasting monuments and for trim and decoration on buildings.
SCORIA Scoria rocks are igneous rocks which were formed when lava cooled quickly above ground. You can see where little pockets of air had been. Scoria is actually a kind of glass and not a mixture of minerals.
PUMICE Pumice rocks are igneous rocks which were formed when lava cooled quickly above ground. You can see where little pockets of air had been.
PUMICE Pumice rock is so light, that many will actually float in water. Because this rock is so light, it is used quite often as a decorative landscape stone. Ground to a powder, it is used as an abrasive in polish compounds and in Lava© soap.
OBSIDIAN Obsidian rocks are igneous rocks that form when lava cools quickly above ground. Obsidian is actually glass and not a mixture of minerals. The edges of this rock are very sharp.
GEOLOGIC PROCESSES The San Andreas Fault is an example of a transform fault. Figure 15 -5
WEARING DOWN AND BUILDING UP THE EARTH’S SURFACE Weathering is an external process that wears the earth’s surface down. Figure 15 -6
Parent material (rock) Biological weathering (tree roots and lichens) Chemical weathering (water, acids, and gases) Particles of parent material Physical weathering (wind, rain, thermal expansion and contraction, water freezing) Fig. 15 -6, p. 340
MINERALS, ROCKS, AND THE ROCK CYCLE The earth’s crust consists of solid inorganic elements and compounds called minerals that can sometimes be used as resources. Mineral resource: is a concentration of naturally occurring material in or on the earth’s crust that can be extracted and processed into useful materials at an affordable cost.
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