Sands and Sandstones

Sands and Sandstones - Sands are loose, unconsolidated rocks having particle sizes between those of silt and pebbles (1/16 mm to 12mm).   When held together by chemical cement or by clay, they are called sand- stones. These rocks result from the breaking down or weathering of older rocks, and from the transportation and sorting of the rock fragments by moving water or by wind.

 Sand mostly consists of grains of quartz, but some of it may contain large amounts of feldspar. Sand occurs almost everywhere along large stream valleys, in regions of old glacial drainage or out wash.

 Sandstones, like sand, consist largely of quartz grains, but sandstones are held together by some natural cement or matrix such as calcium carbonate, iron oxide, or clay, and the rocks can be classified according to the type of cement. Interesting collections of sandstones in which the grains are cemented by different types of material have been made. In places, sand- stone occurs intersected with shale and limestone, in other places, it occurs as channel deposits cutting through shale and limestone. Sandstone that is buff or brownish in color is cemented with iron oxide. There are areas of sandstone cemented by calcite (calcium carbonate) in crystals so large that wide areas of the rock reflect light in a manner known as "luster mottling.''

This rock is sometimes called ''quartzite'' because it is very hard, but it is not a true quartzite. In other areas, soft, crumbly sandstones from the cretaceous age form cliffs and box canyons.

 Sand Asphalt - It is either:   1) A hot-laid plant mix mixture of local sand and asphalt cement prepared without special control of aggregate grading; or 2) A mixture of local sand, with or without mineral filler, and a liquid asphaltic material. In the latter case, either road mix or plant mix construction may be employed. Sand asphalt is used in low-cost construction for both base and surface courses. It is known as the fine aggregate type of mixture.

  Sand Clay - (Road Surface) A surface composed of a mixture of sand and clay where the two materials have been blended, so that their opposite qualities tend to maintain a condition of stability, under varying moisture content. Some deposits are found in nature, but the bulk of such surfaces are prepared artificially.

 Sandstone - An indurated sedimentary rock formed of coherent or cemented sand.

The following are common varieties:  Asphaltic sandstone, Bluestone, Brownstone,

Building sandstone, Flagstone and Free-stone.

 Scalping - An operation in which 85 to 95 percent of feed material is considerably smaller than the screen opening.

 Scalping Screen - A vibrating or revolving screen which separates various sizes of materials for delivery to one or more crushers and bypasses small sizes around the crushers.

 Serpentine - 1) In mineralogy, a hydrous magnesium silicate (H₄Mg₃Si₂O₈), commonly green, greenish-yellow, or greenish- gray, and massive, fibrous, lamellar, or occurring as pseudomorphs. It is an important constituent of some metamorphic rocks and is everywhere secondary, after olivine, amphibole, pyroxene, etc. 2) In petrology, a metamorphic rock composed chiefly or wholly of the mineral serpentine. (La Forge)

 Schist – A crystalline rock that can be readily split or cleaved because of having a foliated or parallel structure, generally secondary and developed by shearing and recrystallization under pressure. (La Forge)

Screenings - Fine material that passes through a screen when screening for lump material.

 Screening Efficiency - Ratio of screen undersize actually passing the screen openings to the total undersize in the feed.

Shale - A hardened, compacted clay or silt which breaks along bedding planes is called shale. The particles that make up a shale are too small to be seen without a microscope. Shales have a leaflike bedding and weather into thin slabs or plates, some of which are no thicker than paper. When shales weather, they form clays or muds. Shales and clays are easily eroded or worn away. Consequently, the best exposures are found underneath ledges of harder, more resistant rocks such as limestones and sandstones. Most shales are soft enough to be cut with a knife and are rather brittle or crumbly. The usual color is gray, but black, green, red, or buff shales are common. Many shales contain nodules of pyrite, selenite crystals, or in concretions of various forms. Shale and clay together make up about 80% of the sedimentary rocks of the earth's crust. Some black, very thin bedded shales are often called slate because they have the same color as many slates and because they break Into thin, hard platy sheets. Slate, however, is a metamorphic rock formed when shale is put under great heat and pressure.

Shell - The term "Shell  Aggregate'' applies to oyster, clam shells, etc., used for road surfacing material. These shells are crushed in an ordinary stone crusher. It is difficult to crush this material to a given specification,   and it does not produce a strong pavement unless a suitable gradation is produced through the introduction of other aggregates, such as sand and stone.

Siderite - Siderite, which is a common mineral, is composed of iron carbonate (FeCO₂). It is light to dark brown, and some of it occurs as rhomb-shaped crystals with curved faces (like dolomite). Most siderite is granular or earthy. The mineral cannot be scratched by a knife. It fizzes in hot hydrochloric acid, but reacts slowly in cold acid. Weathered surfaces change to limonite   and turn dark brown.

Silica - An oxide of silicon, (SiO₂). Occurs in nature as a mineral of economic importance in quartz, chalcedony, chert, flint, opal, diatomaceous earth and sandstone. The most abundant constituent of the earth's crust. See also Agate, Quartz. Also known as silex, and used for lining tube mills.

Silt and Sandstone - Silt is a common sedimentary rock composed of tiny particles smaller than sand size, yet larger than clay size (1/16mm to 1/256mm). It is found in stream deposits and lake beds, but it occurs chiefly as a windblown deposit called loess. It is typically a yellowish buff porous silt that crops out with steep faces along hillsides and valley wails. Much loess contains white or cream colored concretions an inch or two in diameter, which are composed of calcium carbonate and have been called Kindchen (little children) of the loess. Small white shells of snails may also be found in the loess.

Some of the finest and thickest soils in the world are formed in the upper pad of thick deposits of loess. As wind moves small particles only, a soil built up from deposits of this kind is free from rocks and large pebbles. Loess deposits have been built up by successive dust storms.

Consolidated or compacted silt is known as siltstone. This rock may be found as thin, slabby beds in many of the Pennsylvanian formations. Many siltstones and fine sandstones contain layers rich in tiny flakes of mica, which glitter in the sun. The mica is concentrated along the bedding places where the rock breaks easily.