Things You Should Know About Shale Rock

Shale is a sedimentary rock which is 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 a predominant characteristic of this sedimentary rock type. In fact, it is this feature that distinguishes shale from other mudstones with similar composition.

Shale is made up of mud, which comprises clay minerals and traces of minerals like quartz and calcite. The grains of these minerals 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 this rock.

Owing to its fissility, these rocks split unevenly, but parallel to the bedding plane. As with various other sedimentary rocks even shale has a smooth 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.

Sedimentary rocks form by the means of sedimentation; shale is no exception. In its case, the formation process is referred to as 'compaction', wherein fine grains get consolidated at the rock bed over the years and compose the rock. Being very fine in nature, the particles that form shale float in water a long after other dense particles settle down.

Owing to the tendency of these particles to settle in slow-moving water, the formation of this rock is most often observed in lakes, river deltas, flood plains, and even in deeper regions of continental shelf where water is relatively calm at times.

When this rock is subjected to intense heat and pressure, it undergoes the process of metamorphism and turns to a metamorphic rock type known as the slate.

Shale predominantly contains clay minerals and fine grains of quartz or calcite, owing to which it gets its gray color. Clay minerals present in it include kaolinite, montmorillonite, illite, etc. Minor traces of chert, calcite, dolomite, ankerite, hematite, etc., are also seen in this rock. The varying amount of these minor constituents in the rock determine its color.

Generally, gray color is predominant, but colors like red, yellow, brown, and 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 clay to a great extent. Owing to its various characteristics, shale has become an important constituent of our numerous requirements.

Among its various uses, its use in brick kilns is perhaps the most popular. It is also an important component of cement used in construction.