Why is sandstone useful

Following crushing, the material may report to a secondary or tertiary crushing plant. The sized material is then transported to a processing plant, usually by a conveyance system. Dimension stone is any rock material that is cut into specific sizes, typically as blocks and slabs. Crushed stone is used in the construction of roadways and road structures such as bridges, and in buildings, both commercial and residential. Skip to content Return to Minerals Database.

Type Rock. Pure quartz sands that are well sorted can rarely be compacted to any large extent, and compaction in these sands will not result in lithification. Poorly sorted sands, one the other hand, may contain a significant fraction of clay minerals. Clay minerals are ductile, and can deform around the sand grains during compaction, thus reducing the porosity and starting the process of lithification.

Due to changes in pressure, temperature, and composition of the fluid phase, some minerals recrystallize, i. Such textural changes may result in stronger lithification of the sediment. Solution is the process of dissolving mineral matter.

As fluids pass through the sediment, unstable constituents may dissolve and are either transported away or are reprecipitated in nearby pores where conditions are different. One processes whereby grains are dissolved is called pressure solution. Pressure solution occurs at zones of grain-to-grain contact where pressure is concentrated. Dissolution of the grains preferentially occurs along these higher pressure areas and the dissolved ions migrate away from the point of contact toward areas of lower pressure where the dissolved ions are reprecipitated.

Most lithification is the result of new authigenic minerals forming in the pore space to create a cement which holds the grains together. The most common cements are quartz, calcite, clay minerals, and hematite, although other minerals like pyrite, gypsum, and barite can also form cements under special geologic conditions.

Quartz cement often occurs as overgrowths on the original quartz grains. These overgrowths grow in crystallographic and optical continuity with the original quartz grains. The overgrowth cement grows outward from the original grain until it runs into cement growing outward from an adjacent grain.

Thus, the rock attains a texture of interlocking grains similar to an igneous crystalline granular texture. If the grain has small specs of clay or other fine grained dirt forming an irregular coating on its surface, the coating may be preserved and show the original outline of the grain.

Often times when these cements form near the Earth's surface, the cementing minerals form crystallographically continuous crystals in the cement, resulting in Sand Crystals. Such crystals are usually made mostly of grains of quartz sand, but have the appearance of a crystal like a barite rose, a gypsum rose, or calcite crystal only because the cement between the grains forms a crystal. If you were to cut a thin section of such a sand crystal you would see that the cement is optically continuous between the grains i.

Although there are many replacement phases, dolomite, opal, quartz, and illite are some of the most important. Petrified wood is an excellent example of replacement. There are several reasons for this: Quartz is one of the most abundant minerals in crystalline rocks like granitoids, schists, and gneisses. Quartz is mechanically durable due to its high hardness and lack of cleavage.

Quartz is chemically stable under conditions present at the Earth's surface. It has a very low solubility in water. Although feldspars are the most common minerals in igneous and metamorphic rocks, feldspars are less stable than quartz at conditions near the Earth's surface. Feldspars in sandstones consist of the following: Plagioclase - usually showing albite twinning.

Such plagioclase can be derived from both igneous and metamorphic sources. If the plagioclase also shows zoning, then it is likely from a volcanic source. Alkali Feldspar - Orthoclase and microcline are derived from both igneous and metamorphic sources. Sanidine is derived from volcanic sources. Microperthite, the intergrowth of K-rich and Na-rich alkali feldspars, is likely derived from a plutonic igneous source.

Lithic Fragments. With the exception of fragments of polycrystalline quartz, lithic fragments are generally unstable in the sedimentary environment, yet, if present in a sandstone give the best clues to provenance. Any type of rock fragment can be found in a sandstone, but some kinds are more common due to the following factors: Areal extent in the source drainage basin.

The greater the outcrop area of the source that produces the lithic fragment, the more likely it is to occur in sediment derived from that source. Location and relief of the drainage basin. If the source is located close to the depositional basin, lithic fragments derived from the source are more likely to occur in the sediment.

If the source area has high topographic relief, rates of erosion will be higher, and lithic fragments derived from the source will be more likely to occur in the sediment. Stability of the rock fragment in the sedimentary environment. Fragments of mudrocks are relatively rare due to their mechanical weakness during transport.

Similarly fragments of gabbros are rare in sandstones because the minerals they contain are chemically unstable in the sedimentary environment. Because sandstones are usually cemented together with calcite or hematite, sandstone fragments break down easily during transport. The minerals that occur in granites, however, are more stable under conditions present near the Earth's surface, and thus granitic fragments are more common in sandstones.

Volcanic rock fragments, with the exception of crystalline rhyolites, are generally unstable, but may occur if factors 1, 2 and 4 are favorable. Size of the crystals in the fragments. In order to be present in a sandstone as a lithic fragment, the grain size of the minerals in the lithic fragment must be smaller than the grain size of the sediment.

Thus, granitic fragments will be expected to be rare, except in coarse sands, and volcanic and fine-grained metamorphic fragments will be expected to be more common. The sediment particles are clasts, or pieces, of minerals and fragments of rock, thus sandstone is a clastic sedimentary rock. It is composed mostly of sand particles, which are of medium size; therefore, sandstone is a medium-grained clastic sedimentary rock.

The sand grains that makeup sandstone are aptly referred to as framework grains. Sandstone may include finer and coarser material and still be called sandstone, but if it includes more than 30 percent grains of gravel, cobble or boulder size it's classified instead as conglomerate or breccia together these are called rudites.

Sandstone has two different kinds of material in it besides the sediment particles: matrix and cement. Matrix is the fine-grained stuff silt and clay size that was in the sediment along with the sand whereas cement is the mineral matter, introduced later, that binds the sediment into rock.

Sandstone with a lot of matrix is called poorly sorted. If matrix amounts to more than 10 percent of the rock, it is called a wacke "wacky". A well-sorted sandstone little matrix with little cement is called an arenite. Another way to look at it is that wacke is dirty and arenite is clean. You may notice that none of this discussion mentions any particular minerals, just a certain particle size.

But in fact, minerals make up an important part of sandstone's geologic story. Sandstone is formally defined strictly by particle size, but rocks made of carbonate minerals don't qualify as sandstone. Carbonate rocks are called limestone and given a whole separate classification, so sandstone really signifies a silicate-rich rock. A medium-grained clastic carbonate rock, or "limestone sandstone," is called calcarenite. This division makes sense because limestone is made in clean ocean water, whereas silicate rocks are made from sediment eroded off the continents.

Mature continental sediment consists of a handful of surface minerals , and sandstone, therefore, is usually almost all quartz. Other minerals—clays, hematite, ilmenite, feldspar , amphibole, and mica — and small rock fragments lithics as well as organic carbon bitumen add color and character to the clastic fraction or the matrix. A sandstone with at least 25 percent feldspar is called arkose. A sandstone made of volcanic particles is called tuff. The cement in sandstone is usually one of three materials: silica chemically the same as quartz , calcium carbonate or iron oxide.

These may infiltrate the matrix and bind it together, or they may fill the spaces where there is no matrix. Depending on the mix of matrix and cement, sandstone may have a wide range of color from nearly white to nearly black, with gray, brown, red, pink and buff in between. Sandstone forms where sand is laid down and buried. Usually, this happens offshore from river deltas , but desert dunes and beaches can leave sandstone beds in the geologic record too.

The famous red rocks of the Grand Canyon, for instance, formed in a desert setting.