Sandstone – Meaning, Uses, Facts, Properties & Color

 

What is Sandstone?

Sandstone is one of the most common kinds of clastic sedimentary rocks consists of sand-size (0.06 to 2 mm) clasts or grains of minerals and organic matter.

Formation of Sandstone

The formation of sandstone occurs mostly in two phases, sedimentation/accumulation & compaction. Sedimentation of sand particles takes place either through water or air. Compaction occurs with physical pressure and chemical changes. The steps are:

1. Sedimentation of quartz crystals
2. Formation of cement & matrix
3. Formation of pores

Types of Sandstone Components

The first phase forms sand clasts or grains due to the transportation of sand particles from the source. The second phase forms cement or binding material and matrix as filler between the framework grains or clasts. The pore space is a void where no clasts, cement, or matrix matter exists. Let’s know these components of sandstone with some details.

Grains or Clasts in Sandstone

• Clasts, also known as framework grains. Based on grain size, we can classify clasts into three categories:
• Fine-grains – 0.06-0.2mm
• Mid-grains – 0.2-0.6mm
• Coarse-grains – 0.6-2mm
• Based on the mineral compositions of the clasts, we can divide them into the following categories:
• Quartz Grains, which predominantly contain quartz minerals with long survival capacity.
• Feldspar Grains, which are found as either alkali or Plagioclase feldspar.
• Lithic Grains, which are maybe from igneous, metamorphic, or sedimentary rocks.
• Accessory mineral includes micas, olivine, pyroxene, and corundum. These are forming a highly dense mass that renders sandstone a mature one.

Cementing Material in Sandstone Structure

• Cementing means binding. The cementing material in sandstone structure binds clastic framework grains or clusters of grains to gather firmly and becomes responsible for strength, durability, and wear & tears.
• Cement is the secondary material, which forms after sedimentation or deposition of grains.
• Based on the predominance of mineral types, we can classify cement in sandstone the following ways.
• Siliceous Cement– It has silica or quartz particles that give the strongest bonds.
• Calcareous Cement – It has calcites, and forms in patches leaving gaps open, so it makes sandstone porous.
• Argillaceous Cement – It has clay particles, and forms softer types of sandstone.
• Ferruginous Cement – It has ferrous content. So, it also is known as Hematite cement and gives reddish hues.

Matrix of Sandstone

• It is fine material.
• It founds within interstitial pore space among the framework grains of sandstone.
• Arenite sandstones contain very little amount of matrix, so those are clean type.
• Wackes are consisting of an abundance of the matrix, so those are dirty types of sandstone.

Pore Space in Sandstone

• Pores are open spaces within the rock mass. It gives porosity or permeability property to the sandstone rocks.
• Some sandstone types have tightly packed pores while some have loose binding between the clusters.
• The occurrence of pores defines the porous nature of sandstone.

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