Aqueous Rocks Examples (Characteristics and Types)

In this article, you’ll get to know some commonly known aqueous rocks, as well as information about aqueous rocks to better understand them.

Aqueous Rocks Examples (Characteristics and Types)

What are Aqueous rocks?

Aqueous rocks are a specific type of sedimentary rock that is formed through a process known as sedimentation, which takes place in water that moves sediment material around until it ends up in a calm enough location that it can settle and form into a mass.

The sediment materials vary in particle size and substance.

These materials swirl together and mix with iron oxide, silica or lime substances, forming a cement-like mixture.

Sedimentary rocks tend to consist of materials that previously existed before they were formed, either on or below the earth’s surface.

As the materials are moved around by tectonic movement, volcanic eruption or shifting water sources, they form into new rocks.

This means that aqueous rocks mostly contain secondary minerals and small amounts of primary minerals.

Some of the types of rock that are formed this way include shale, limestone and sandstone.

There are a number of names used to describe aqueous rocks, some of which are old and outdated terminology but a few are still used.

One of these terms comes from how aqueous rocks tend to be deposited at various depths of the strata layers and thus are often called stratified rocks.

Another term used to describe many aqueous rocks is argillaceous rocks.

What are Argillaceous Rocks?

Argillaceous rock deposits are one of the most abundant types of sedimentary stone and include various types of rocks known as lutites (any fine-grained, sedimentary rock that contains silt and clay sediment or both), including mudstone, shale, argillite, claystone and siltstone.

When mixed with water, lutites often turn to mud.

Argillaceous also describes rocks that contain secondary components of clay minerals such as argillaceous limestone.

These are stones that are mostly made up of calcium carbonate with at least 10% of their material being clay and other fine mineral particle fragments of a specific size range (below 0.002 mm diameter).

Another example of this kind of stone is argillaceous sandstone, which is mostly made up of fine grains of quartz crystals and small amounts of clay minerals.

While there is some commercial use for argillite in the mixing of concrete, the rest of the argillaceous rocks have little commercial use.

Where they lack in commercial use, they make up for it by being an indicator for other precious resources like gas and water in clay beds.

They also serve as a warning to miners and tunnel builders as the presence of large amounts of argillaceous materials as toxic or explosive gases can leak out of pockets between the material layers.

This can pose a serious hazard if not properly ventilated.

What are some examples of Aqueous or Argillaceous rocks?

Mudstone

Mudstone is a sedimentary rock made from fine clay and mud particles and tends to form in large blocky masses.

This term can also be used to describe carbonate rock types such as limestone and dolomite, but is more commonly used when referring to mudstones that mostly contain silicate minerals.

What constitutes a mudstone is largely debated and there does not seem to be any agreed upon definition, but it is agreed mudstones contain fine sedimentary particles that are primarily silicate grains measuring 0.063 mm.

This means that due to the microscopic nature of the materials that make mudstone, the classification refers more to the texture than the composition of materials.

Visually, mudstone resembles hardened clay and may have visible fissures and cracks on its surface.

Argillite

Argillite is a sedimentary rock that is made of primarily indurated clay minerals, more so than even claystone itself or even shale.

Argillites are essentially underdeveloped shale that has not transformed to have the fissile layers that are present in shale.

Argillites usually have high amounts of silica, alkali and aluminium in their composition.

When argillite goes through metamorphic changes, it can produce a number of different materials, such as schist, slate and phyllite.

Shale

Shale is a clastic sedimentary rock made of small silt and clay grains that have been compressed over time, layer by layer.

Each layer is quite thin and is prone to breaking apart where these layers meet when strained.

Shale also contains a variety of mineral particles and organic materials.

Varieties of shale include black, organic-rich and calcareous.

Black shale is unique among these as it gets its color from the organic carbon in its makeup.

Black shale contains more than 1% organic carbon and can be as much as 20%.

This makes it a great source of hydrocarbons (oil & gas).

Shale is often used as the generic reference to describe both aqueous and argillaceous rocks in casual conversations.

Siltstone

Siltstone is a mudrock that has low amounts of clay minerals and is distinguishable from its cousin, shale, by its inability to split apart along the flat planes of its layers (lack of fissility).

This sedimentary rock is clastic in nature and made mostly of silty quartz material (primarily thought to come from glacial grinding) and is sometimes referred to as aleurolite.

Siltstone, while not a typical source of hydrocarbons, can sometimes have pockets of gas trapped inside it.

In this case, the method of extraction is through hydraulic fracturing (fracking).

Siltstone was a valued material in the ancient world, where it was used in the making of sculptures in Egypt.

Limestone

Composed primarily of the calcium carbonate crystals calcite and aragonite, limestone is considered a carbonate sedimentary material which mostly forms in shallow marine environments.

It is common to find fossils in limestone deposits, which allows us a glimpse into the history of life on our planet and how it has evolved over time.

It is thought that upwards of 25% of the planet’s sedimentary rocks are carbonate in nature, with the bulk of them being limestone.

Limestone has a number of commercial uses, including in the making of cement, road construction, pigment for products like paint and toothpaste and soil conditioning.

It also varies in color depending on the organic material present in the deposit. Colors range from white to grey and, in organic rich deposits, black.

Sandstone

Sandstones are primarily made of quartz and feldspar.

These two minerals are highly weather resistant and withstand even the harshest conditions on earth’s surface.

It varies in color widely depending on the trace materials that are captured in the forming process of the deposit.

You can find the following colors all over the world: red, black, brown, blue, pink, yellow, black, white, orange and tan.

Sandstone has been used as an indicator for finding water sources due to its porous nature and the ability for water to become trapped within.

This is also true when it comes to finding petroleum.

Conglomerates

This is a term given to sedimentary rock which is made from a mixture of gravely materials and finer sedimentary grains like silt, sand and clay.

All of these are fused together in a rough amalgamation with hardened clay and other mineral compounds.

Conglomerates tend to be found in all sedimentary layers, but overall, do not make up a significant percentage of the total sedimentary material of the earth’s crust.