Shale Rock

Shale is a sedimentary rock typically characterized by fine laminations, that are parallel to the bedding plane. The process by which these rocks break along the thin laminae is referred to as fissility, which is yet another predominant characteristic of this sedimentary rock type. In fact, it is this feature that distinguishes the shale rock from other mudstones, which are similar to the shale as far as their composition is concerned.

Shale Rock Facts

The shale is made up of mud, which comprises clay minerals and traces of minerals like quartz and calcite. The grains of these minerals, like quartz and calcite, are so fine, that they can be only seen with the help of a microscope. The varying ratio of the clay minerals to the other minerals determines the physical attributes of the shale rock. Owing to their fissility, these rocks tend to split unevenly but parallel to the bedding plane. As with various other sedimentary rocks even shale is smooth in terms of texture. In fact, you can scratch this rock with the help of a knife. It tends to breaks in flakes when subjected to immense weathering.

Formation
Sedimentary rocks form by the means of sedimentation. In case of shale, the process of its formation is referred to as 'compaction', wherein fine grains which compose the rock get consolidated at the rock bed over the years. Being very fine in nature, the particles which form shale tend to float in water a long after the other dense particles settle down. Owing to the tendency of these fine particles to settle in slow moving water, shale rock formation is most often observed in lakes, river deltas, flood plains and, at times, even in deeper regions of continental shelf, where water is relatively calm. When this rock is subjected to intense heat and pressure, it tends to undergo the process of metamorphism, and turns to a metamorphic rock type known as the slate.

Composition
These rock predominantly contain clay minerals and fine grains of quartz or calcite, owing to which they get their gray color. The clay minerals present in these rocks include kaolinite, montmorillonite, illite etc. Minor traces of chert, calcite, dolomite, ankerite, hematite etc are also seen in shale rocks. The varying amount of these minor constituents in the rock determine its color. Generally, gray color is predominant, but colors like red, yellow, brown, green are also observed. Red color indicates the presence of hematite, brown color indicates the presence of goethite and green color indicates the presence of chlorite. The black color, on the other hand, is attributed to the presence of carbonaceous material in it. This is also a sign of the process of oxidation-reduction.

Even though this rock is predominantly made of clay, it plasticity to water differentiates it from the clay to a significant extent. Owing to its various characteristics, shale rock has become an important constituent of various requirements of mankind. Among its various uses, its use in brick kilns where bricks are manufactured is perhaps the most popular. It is also an important component of cement used in construction.