Our earth is constantly changing. Land masses are being formed and broken down as a part of a process known as the rock cycle. The earth is made of several layers. The core is a solid mass at the center of our planet. Surrounding the core is the mantle. It is the thickest layer and consists of elements. The crust is a thin layer of material that sits on top of the mantle and is exposed to our atmosphere. The rock cycle begins in the mantle of the Earth.
The Earth's crust is made up of about 20 large parts or plates. Because the crust sits on top of a mass of material (the mantle) so hot that it is soft or plastic, it is always moving—a concept called plate tectonics. This movement pushes and pulls the crust into mountains creating cracks and unstable places, often resulting in earthquakes. The movement also generates heat which melts the surrounding rock into magma that combines with the "plastic" material in the mantle. Sometimes the magma flows into pockets below the surface of the Earth while at other times the magma leaks out of the cracks forming volcanoes.
Magma sometimes flows into subsurface pockets. As it slowly cools, it becomes igneous rocks. Molten material coming from a volcano, now called lava, cools as it reaches the surface of the earth and also forms igneous rocks. These rocks consist of elements which have combined to form minerals.
Rocks made through volcanic action are called igneous rocks because they were formed in the fire of the volcano from which they came. As soon as a rock is formed, the action of weather, water, heat, and pressure in some combination begins to break it down. When weather, water, and pressure break down an igneous rock, soil is eventually formed. Soil and small rocks that are compacted together through pressure and water form sedimentary rocks. Sedimentary rocks are continuously being made and broken down through the action of weather, water, and pressure. Sometimes an igneous or sedimentary rock is subjected to extreme heat and pressure that changes its original composition. The resulting rock is called a metamorphic rock because it has been changed. Metamorphic rocks are continuously being formed and broken down by the action of weather, water and pressure.
A native metallic element. It is copper red when fractured but may be greenish, bluish or tarnished if weathered. This element is heavy, ductile, and malleable. Copper is not usually found in its pure or native form in the crust of the earth. Most often, the element has been combined through volcanic action with other elements to form minerals that contain copper and other substances. The names and descriptions of some of the most common copper minerals follow:
Usually a bright green in color with a non-metallic luster. It has a light green streak and can always be scratched with a knife. Malachite, a copper carbonate, is an important ore of copper and is a good indicator of copper deposits. In its pure form it contains 57% copper, and the rest is made up of carbonate and water.
A copper carbonate. Its streak is light blue. Malachite and azurite frequently occur together and are found in the upper weathered (oxidized) zones of copper ore bodies. Azurite is the scarcer of the two and has a soft to deep blue color.
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A copper silicate. It is bright blue or green in color with a white to pale blue or green streak. Chrysocolla frequently occurs with azurite and malachite. It is an important copper oxide mineral.
An iron copper sulfide. It has a brass yellow color. It is distinguished from pyrite by being softer and more yellow. The yellow color comes from the sulfur contained in the mineral. Its golden glint when in small specks in quartz often is mistaken for gold. The glint will disappear when turned at certain angles to the light while gold appears the same at all angles. Chalcopyrite is the primary mineral of copper and is prevalent wherever copper ore is being mined below the surface zone.
A copper sulfide. It is one of the highest grades and most important minerals of copper and is opaque with a dark lead gray to black color. Chalcocite is often associated with and shows alteration to azurite, malachite, and native copper, as well as other minerals. Important deposits are found in Arizona's Bagdad, Jerome, and Superior areas as well as in other states.
A copper-iron sulfide. Its color is a natural bronze, but on exposure it tarnishes to the variegated colors that have caused it to be nick-named "peacock ore." It is rarely found on the surface but is prevalent in deeper levels of copper mines.
A hydrous aluminum phosphate with copper. The color is due to the presence of copper. It is found near the surface of copper deposits. Sometimes it may appear as an outcrop. To be desirable as gems the color should be greenish blue.
Copper minerals are formed at various depths in the earth's crust. Sometimes they are exposed to air and water. When this happens the copper mineral is said to be oxidized which changes its chemical composition. Azurite, malachite, chrysocolla, and turquoise, are copper oxide minerals. Copper sulfide minerals are those that have not been exposed to air and water. Chalcopyrite, chalcocite, and bornite are sulfide minerals.
Copper has been used since the Stone Age because it has unique properties which make it usable in a wide variety of ways. It is ductile, which means that it can be pulled into a very thin wire. Copper is also malleable, which means that it can be bent or hammered into many shapes and very thin sheets without breaking or coming apart. It resists corrosion, standing up to weather and chemicals, and it conducts heat and electricity better than any other metal except silver. In addition, copper's reddish color makes it an important metal for ornamentation. Thus, throughout history copper has been a versatile, valuable, and vital metal.
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