Because it is so dense and resistant to both physical and chemical weathering, it is a poor bedrock on which to form soil. As a result, typically-quarried quartzite is very near the surface. Because it is so hard and dense, quartzite has not been quarried as extensively as other softer dimension stone such as limestone, sandstone and granite.
These generally have supported the mining economy of Idaho over the last years, but their importance is decreasing. These veins are formed when sulfide minerals fill void spaces in cracks or shear zones. Coeur d'Alene District: The Coeur d'Alene district in northern Idaho is one of the major lead-zinc-silver producing areas of the world. Since mining began in the early s, mines in the square-mile district have produced more than 2. The country rock host rock consists of six formations of the fine-grained, siliceous, Precambrian Belt Supergroup.
The sediments are intruded by several types of small stocks and dikes. The structural geology of the area is complicated by a variety of folds and faults of diverse acres and movements. The district is at the intersection of the west-northwest-trending Osburn fault and a north-trending anticlinal uplift. Six periods of mineralization ranging in age from Precambrian to Tertiary have been identified. The main period of mineralization probably occurred during the Late Cretaceous.
The productive veins, apparently controlled by deep fractures, trend northwesterly. Although many veins crop out at the surface, some apex several thousand feet below the surface. Depth appears to have had little effect on the occurrence or type of ore. DeLamar Silver Mine in Southwestern Idaho: Gold was discovered in the DeLamar area in ; however, production, primarily by underground mining, terminated in The exploration phase for the DeLamar silver mine began in and by open pit mining was started.
In , ore reserves totaled approximately 11 million tons, averaging 1. Approximately 27, tons of ore and waste are moved each day, of which 3, tons are ore. Current production includes about 1. The silicic volcanics and subsequent mineralization were controlled by large normal faults. Such conditions fuse the quartz grains together forming a dense, hard, equigranular rock.
The name quartzite implies not only a high degree of induration hardness , but also a high quartz content. The uses of quartzite and some reasons that it is avoided are summarized below. In architecture, marble and granite have been the favorite materials for thousands of years. Quartzite, with a Mohs hardness of seven along with greater toughness, is superior to both in many uses. It stands up better to abrasion in stair treads, floor tiles, and countertops.
It is more resistant to most chemicals and environmental conditions. It is available in a range of neutral colors that many people enjoy. The use of quartzite in these uses is growing slowly as more people learn about it. There are also man-made materials marketed under the name quartzite. They can be attractive and durable with a cost comparable to natural materials. Read the marketing materials prepared by the manufacturer. Quartzite can be an extremely durable crushed stone that is suitable for use in the most demanding applications.
Its soundness and abrasion resistance are superior to most other materials. Unfortunately, the same durability that makes quartzite a superior construction material also limits its use. Its hardness and toughness cause heavy wear on crushers, screens, truck beds, cutting tools, loaders, tires, tracks, drill bits, and other equipment. As a result, the use of quartzite is mainly limited to geographic areas where other aggregates are not available.
Quartzite is valued as a raw material because of its high silica content. These are mined and used to manufacture glass, ferrosilicon, manganese ferrosilicon, silicon metal, silicon carbide, and other materials. Quartzite can be a very attractive stone when it is colored by inclusions. Inclusions of fuchsite a green chromium-rich variety of muscovite mica can give quartzite a pleasing green color.
If the quartzite is semitransparent to translucent, the flat flakes of mica can reflect light to produce a glittering luster known as aventurescence. Material that displays this property is known as " aventurine ," a popular material used to produce beads, cabochons, tumbled stones , and small ornaments. Aventurine can be pink or red when stained with iron. Included dumortierite produces a blue color.
Other inclusions produce white, gray, orange, or yellow aventurine. Quartzite has been used by humans to make stone tools for over one million years. It was mainly used for impact tools, but its conchoidal fracture allowed it to be broken to form sharp edges. Broken pieces of quartzite were used for crude cutting and chopping tools. Quartzite was not the preferred material for producing cutting tools such as knife blades and projectile points - but it has been used.
Flint , chert , jasper, agate , and obsidian all can be knapped to produce fine cutting edges, which are difficult to produce when working quartzite. Quartzite was most frequently used when it was locally abundant and superior materials were rare or not available.
Article by: Hobart M. Find Other Topics on Geology. Maps Volcanoes World Maps.
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