You might have heard the word Siltstone during the conversations with contractors and stone suppliers, but you are not aware of it entirely. Despite its scanty supply, Siltstone is still having great significance in the construction industry and useful in exterior applications. Let’s learn about it in detail.

What Is Siltstone:

Siltstone is a fine-grained sedimentary rock predominantly (more than 2/3) consists of consolidated silt-sized particles like Coarse silt – 1/32mm (5Phi-Ø); Fine silt – 1/64mm (6Phi-Ø); Very fine silt – 1/128mm (7Phi-Ø) and used to break into thin chips, which are running roughly parallel from top to bottom.

  • Siltstone differs from sandstone because of smaller pores.
  • Siltstone differs from a shale due to missing fissility and laminations that shale stone has.
  • Siltstone differs from the mudstone or claystone thanks to a lower proportion of clay particles in its composition.

Classification of Siltstone at Geological Point of View:

Geologists generally classified Siltstone in the following ways.

Class Sedimentary rocks
Sub-class Durable & hard rock
Categories Fine-grained & opaque rock
Species 35 recognized clay minerals exist.

Properties of Siltstone:

  • Siltstone is uniform in general.
  • It subtly consolidated into semi-lithified.
  • Lithification and presence of carbonate content give Siltstone a dark appearance. Therefore, most of the marine originated siltstone rocks have a typical appearance of blue-gray to olive green and brown shades.
  • However, the fractured surfaces of Siltstone got stains and look orange-brown to black. 
  • Upon a close examination, we can find local intervals of colluvium but no evidence of the existence of molluscan shells, plant debris, and other fossil materials in siltstone rocks.
  • Siltstone is mostly finding beneath the coarse-alluvium sequence. 
  • The sequence is locating above the basement, which made of various lithologies, such as granites, rhyolite, and meta-sedimentary rocks. 

Other properties of Siltstone at geologists’ perspective are described below in different tables.

The Texture of Siltstone:

The texture and similar properties of siltstones are:

Texture Clastic
Color  A wide range of colors occurs in the Siltstone, such as gray, brown, or reddish-brown. White, yellow, green, red, purple, orange, black, and other colors. 
Durability  Durable 
Water-resistant  Yes 
Scratch-resistant  Yes 
Stain-resistant  No 
Acid-resistant  Yes 
Wind resistant  Yes 
Appearance  Rough 

Construction Properties of Siltstone:

The general properties of Siltstone considered in the construction industry are as follows.

Hardness 6 to 7
Grain size Ranging between 0.0039 and 0.063 millimeters in diameter.
Streak White
Porosity Highly porous
Toughness 2.6
Specific Gravity  2.54 to 2.73
Density 2.6 to 2.7 G/cm3
Specific Heat Capacity 0.92 KL/Kg K
Resistance Heat, Pressure, Water, & Impact-resistant rocks

Composition of Siltstone:

According to the data accumulated by geologists, the structure of Siltstone includes minerals, compound chemicals, and cementing material. Siltstone is a clastic rock. It means it has broken pieces of clasts, weathered rocks, and suspended materials in the sediments.

Mineral content It is a mixture of micas, quartz, feldspars, and clay minerals. Clay is dominating in fine silt whereas, quartz and feldspar are high in the coarse silts.
Compound content Silicon Dioxide (69.2%), Aluminum Oxide (13.8%), Iron (III) Oxide (3.41%), CaO (1.75%), & MgO (2.38%)
Weathering Biological Weathering, Chemical Weathering, & Mechanical Weathering
Erosion  Coastal erosion, water erosion & wind erosion

Weathering of Siltstone observed in the field 

Formation of Siltstone:

_Formation of Siltstone

Siltstone is a sedimentary type of rock. The sedimentation occurred in various environments, including the ancient fresh & marine environment. The particle size of Siltstone is in between the sands & Murdock and somewhat akin to Shell rocks. It means siltstone particles found in a suspension containing clay/mud, shell, and sand particles.

Due to fine-size siltstone particles, the settlement demands quite still and calm water, as in lagoons, dep/big ponds, and puddles on the land. In the ocean, it also demands the same tranquil environment and absence of currents.

Silica and calcium carbonates, like minerals present in the form of solutions, provide the cementing stuff for the formation of siltstones during the sedimentation process.

Where Is Siltstone Found?

The Occurrence of Siltstone:

We know that siltstone formation takes place in the same environment where Shale stone occurs. It means you can locate the deposits of Siltstone at:

  • Around the old delta where the river meets the ocean
  • Deep inland lakes reserve freshwater
  • Lagoons that are forming in the sea must have a calm environment and devoid of oceanic currents
  • Nearby areas of sandstone deposits like adjacent areas of delta edges and sandy beaches 
  • In the fresh or seawater that is still enough to separate silt and clay present within the suspended water solutions

However, Siltstone is among the rarely found rocks and used in the construction industry. The following areas are the main source of commercially applicable siltstone rocks.

applicable siltstone rocks
Asia China, India, Kazakhstan, Mongolia, Russia, & Uzbekistan
Africa Namibia, Nigeria, & South Africa
Europe Austria, Denmark, Germany, Great Britain, Netherlands, Norway, Poland, Sweden, Switzerland, & United Kingdom
North America Canada & USA
South America Brazil 
Oceania New South Wales in Australia & New Zealand

Benefits of Siltstone:

  • Siltstone structure has intergranular pore spaces. So, it serves as a good aquifer construction material.
  • The low porosity of Siltstone renders it useless as an oil or gas reservoir.
  • Siltstone, when locally available, it can substitute as a low-quality fill in the absence of high-quality materials. It means it is a cheaper option in landfilling and as a base material in the construction & road making industry.

Uses of Siltstone:

Siltstone is not a very common rock species in the building industry, but its usefulness is unbeatable in other applications. Let’s take a brief tour of those impressive applications of the siltstone rocks and products.

It has been reported that the White Siltstone quarry from the Eidsvold, Australia is useful in the building construction industry. It has a compressive strength of 44.4MPA. It means it is useful as a landscaping stone as well as suitable for the construction industry.

If you think of dry-stone walling, Siltstone has some marks in human history for it.

Siltstone in Garden Walls & Retaining Walls:

White siltstone veneer from the Eidsvold, Australia, in the construction of garden walls and retaining walls.

Siltstone in Partition Walls:

Eidsvold siltstone in the construction of outdoor partition walls & in the exterior applications.

Siltstone Cladding Bricks for Interior & Exterior Walls:

Cladding bricks from the Eidsvold siltstone. It is useful in the construction of interior and exterior non-load bearing and load-bearing walls.

Siltstone River Pebbles for Home and Landscape Decoration:

Siltstone river pebbles from the Eidsvold, Australia is useful in the interior and exterior decoration, landscaping, and garden beautification.

Siltstone Slabs for Use in Dimension Industry:

Siltstone slabs with Mushroom finish ready for various outdoor paving applications like patios, decks, and paths. 

Siltstone Trench to Drain Excess of Water:

By properties, Siltstone is natural stones, which have low permeability due to low porosity in the mass of rocks. It gives the maximum surface flow to the drainage system created in a natural environment like agriculture fields, wastelands, road/high-way sides, and various hill or mountain areas. 

You can collect the excess of water in the ‘V-shaped’ trench or within an open water drainage system. 

Siltstone Rip Rap:

Siltstone Rip Rap

Siltstone boulders, pebbles, and aggregates can stop the land erosion when appropriately laid in the landscape designing in small to big projects. The construction of rip rap at the seashore, riverbanks, sides of flowing streams, and lakes are using Siltstone due to its low permeability and cost-effective availability. 

Siltstone Resistant Ledge:

A resistant ledge has created from siltstone rocks and aggregates to deflect the water in a creek bed. It helps to accumulate water for irrigation. It allows safe passage to humans and vehicles by creating shallow water depth at the downside of the water stream.

Due to low permeability, Siltstone is a preferred landscaping material when you want to create an impressive waterfall or a creek bed. The above figure indicates that plantation on both sides of awaiting to beautify the entire landscape.

Siltstone in Sculpture:

Human history is full of sculpture made from siltstone rocks.

The first figure is of Nakht-Hor-heb, a military official, holding a shrine made from Siltstone material. The next figure is a natural rock piece purely made from siltstone rock and crafted by Mother Nature itself!

Today, trends of landscape arts are favoring Siltstone as the choice of material where it found abundantly. Fountains, figurines, and other art pieces are not rare now, which made of Siltstone. 

Who Will Be Your Siltstone Supplier?

It is World of Stones USA in Maryland. You can find enough options for siltstone products to use. For example, as dimension stones, natural stone pavers, garden stepping stones, stone veneer for wall cladding, art pieces to decorate your interior or exterior made of Siltstone, and much more in the same line to buy from us. Are you ready for a deal with us for the next project?

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