Non metal mineral resources
Society uses many non-metallic mineral resources, also known as industrial minerals, as well. From the ground, we get the stone used to make roadbeds and buildings, the chemicals for fertilizers, the gypsum in drywall, the salt filling salt shakers, and the sand used to make glass the list is endless. This section looks at a few of these materials and explains where they come from.
Dimension Stone
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| Stone production in quarries. |
The Parthenon, a colossal stone temple rimmed by 46 carved columns, has stood atop a hill overlooking the city of Athens for almost 2,500 years. No wonder“stone,” an architect’s word for rock, outlasts nearly all other construction materials. We use stone to make facades, roofs, curbs, steps, counter tops, and floors. We value stone for its visual appeal as well as its durability. The names that architects give to various types of stone may differ from the formal rock names that geologists use. For example, architects refer to any polished carbonate rock as “marble,” whether or not it has been metamorphosed. Likewise, they refer to any crystalline rocks containing feldspar and/or quartz as “granite,” regardless of whether the rock has an igneous or a metamorphic texture, or a felsic or mafic composition.
To obtain intact slabs and blocks of rock known as dimension stone in the trade for architectural purposes, workers must carefully cut rock out of the walls of quarries (a in figure above). (Note that a quarry provides stone, whereas a mine supplies ore.) To cut stone slabs, quarry operators split rock blocks from bedrock by hammering a series of wedges into the rock, or slice it off bedrock by using a wireline saw, a thermal lance, or a water jet. A wireline saw consists of a loop of braided wire moving between two pulleys. In some cases, as the wire moves along the rock surface, the quarry operator spills abrasive (sand or garnet grains) and water onto the wire. The movement of the wire drags the abrasive along the rock and grinds into it. Alternatively, the quarry operator may use a diamond-coated wire, cooled with pure water. A thermal lance looks like a long blowtorch: a flame of burning diesel fuel, stoked by high-pressure air, pulverizes rock and thereby cuts a slot. More recently, quarry operators have begun to use an abrasive water jet, which squirts out water and abrasives at very high pressure, to cut rock.
To obtain intact slabs and blocks of rock known as dimension stone in the trade for architectural purposes, workers must carefully cut rock out of the walls of quarries (a in figure above). (Note that a quarry provides stone, whereas a mine supplies ore.) To cut stone slabs, quarry operators split rock blocks from bedrock by hammering a series of wedges into the rock, or slice it off bedrock by using a wireline saw, a thermal lance, or a water jet. A wireline saw consists of a loop of braided wire moving between two pulleys. In some cases, as the wire moves along the rock surface, the quarry operator spills abrasive (sand or garnet grains) and water onto the wire. The movement of the wire drags the abrasive along the rock and grinds into it. Alternatively, the quarry operator may use a diamond-coated wire, cooled with pure water. A thermal lance looks like a long blowtorch: a flame of burning diesel fuel, stoked by high-pressure air, pulverizes rock and thereby cuts a slot. More recently, quarry operators have begun to use an abrasive water jet, which squirts out water and abrasives at very high pressure, to cut rock.
Crushed Stone and Concrete
Crushed stone forms the substrate of highways and rail roads and serves as the raw material for manufacturing cement, concrete, and asphalt. In crushed-stone quarries (b in figure above), operators use high explosives to break up bedrock into rubble that they then transport by truck to a jaw crusher. This reduces the rubble into usable chunks.
Most of the buildings and highways constructed in the past two centuries consist of bricks attached to each other by mortar, or of walls, floors, columns, and roads made of concrete that has been spread into a layer or poured into a form. Both mortar and concrete start out as a slurry, but when allowed to set, they harden into a hard, rock-like substance. The slurry from which mortar and concrete form consists of “aggregate” (sand and/or gravel) mixed with water and cement. Before mixing, the cement in mortar and concrete is a powder that consists of lime (CaO), quartz (SiO2), aluminium oxide (Al2O3), and iron oxide (Fe2O3); typically, lime accounts for 66% of cement, silica for 25%, and the remaining chemicals for about 9%. When cement is mixed with water, the chemicals comprising it dissolve. Mortar and concrete set when these chemicals react and a complex assemblage of new mineral crystals grows and binds together pre-existing solid grains in effect, the “cement” in mortar or concrete serves the same purpose as the “cement” in a sandstone or conglomerate.
It appears that the ancient Romans were the first to use cement they made it from a mixture of volcanic ash and limestone. In the 18th and early 19th centuries, cement was produced by heating specific types of limestone (which happened to contain calcite, clay, and quartz in the correct proportions) in a kiln up to a temperature of about 1450nC; the heating releases CO2 gas and produces “clinker,” chunks consisting of lime and other oxide compounds. Manufacturers crushed the clinker into cement powder and packed it in bags for transport. But limestone with the exact composition necessary to make such “cement” is fairly rare, so most cement used today is Portland cement, made by mechanically mixing limestone, sandstone, and shale in just the right proportions, before heating in a kiln to provide the correct chemical make-up. Isaac Johnson, an English engineer, came up with the recipe for Portland cement in 1844; he named it after the town of Portland, England, because he thought that concrete made from it resembled rock exposed there.
Most of the buildings and highways constructed in the past two centuries consist of bricks attached to each other by mortar, or of walls, floors, columns, and roads made of concrete that has been spread into a layer or poured into a form. Both mortar and concrete start out as a slurry, but when allowed to set, they harden into a hard, rock-like substance. The slurry from which mortar and concrete form consists of “aggregate” (sand and/or gravel) mixed with water and cement. Before mixing, the cement in mortar and concrete is a powder that consists of lime (CaO), quartz (SiO2), aluminium oxide (Al2O3), and iron oxide (Fe2O3); typically, lime accounts for 66% of cement, silica for 25%, and the remaining chemicals for about 9%. When cement is mixed with water, the chemicals comprising it dissolve. Mortar and concrete set when these chemicals react and a complex assemblage of new mineral crystals grows and binds together pre-existing solid grains in effect, the “cement” in mortar or concrete serves the same purpose as the “cement” in a sandstone or conglomerate.
It appears that the ancient Romans were the first to use cement they made it from a mixture of volcanic ash and limestone. In the 18th and early 19th centuries, cement was produced by heating specific types of limestone (which happened to contain calcite, clay, and quartz in the correct proportions) in a kiln up to a temperature of about 1450nC; the heating releases CO2 gas and produces “clinker,” chunks consisting of lime and other oxide compounds. Manufacturers crushed the clinker into cement powder and packed it in bags for transport. But limestone with the exact composition necessary to make such “cement” is fairly rare, so most cement used today is Portland cement, made by mechanically mixing limestone, sandstone, and shale in just the right proportions, before heating in a kiln to provide the correct chemical make-up. Isaac Johnson, an English engineer, came up with the recipe for Portland cement in 1844; he named it after the town of Portland, England, because he thought that concrete made from it resembled rock exposed there.
Nonmetallic Minerals for Homes and Farms
We use an astounding variety of non-metallic geologic resources without ever realizing where they come from. Consider the materials in a typical house or apartment. The foundation consists of concrete, made from limestone mixed with sand or gravel. The bricks in the exterior walls originated as clay, formed from the chemical weathering of silicate rocks and perhaps dug from the floodplain of a stream. To make bricks, workers mould wet clay into blocks and then bake it. Baking drives out water and causes metamorphic reactions that recrystallize the clay. The glass used to glaze windows consists largely of silica, formed by first melting and then freezing pure quartz sand from a beach deposit or a sandstone formation. Gypsum board (drywall), used to construct interior walls, comes from a slurry of water and the mineral gypsum sandwiched between sheets of paper. Gypsum (CaSO4s (2O) occurs in evaporite strata precipitated from seawater or saline lake water. Evaporites provide other useful minerals as well, such as halite, and serve as the source for lithium, a key element in computer and camera batteries. Modern technological innovations have also greatly increased the demand for the rare earth elements, a group of 17 elements including the lanthanides, scandium, and yttrium. While the names of rare earth elements are unfamiliar to most people, the elements themselves have become essential in the production of lasers, magnets, X-ray tubes, night vision goggles, camera lenses, and high-tech lamps. Rare earth elements aren't actually that rare, in terms of their abundance relative to other elements in the crust. But localities where ores have a high enough concentration to be mined are rare.
Credits: Stephen Marshak (Essentials of Geology)
Credits: Stephen Marshak (Essentials of Geology)
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