Sandstone
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains. Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any color, but the most common colors are tan, brown, yellow, red, gray and white. Since sandstone beds often form highly visible cliffs and other topographic features, certain colors of sandstone have been strongly identified with certain regions.
 |
| Sandstone |
Sandstones are classified on the basis of the composition of their grains. Three components are considered:
Quartz grainsFeldspar grainsRock fragment grains
Based on the percentage composition of these components, the color and the physical properties of the various varieties of sand stone varies.
Physical Properties of Sandstone
The physical properties of sandstone includes following:
Mineralogy:
A wide variety of rock fragments with up to 75% quartz grains .
Texture:
Medium-grained; may range widely in degrees of grain sorting and shape.
Structure:
Bedding is often apparent along with sedimentary structures and fossils
Occurrence:
Associated with most other sedimentary rock types .
Color:
The color varies from red, green, yellow, gray and white. The variation is result of the binding material and its percentage constituent.
Water Absorption:
The capacity of water absorption is not more than 1.0%
Porosity :
The porosity varies from low to very low.
Density:
2.32 to 2.42 Kg/m3
Hardness:
Lies between 6 to 7 on Moh's Scale
Compressive Strength:
Varies from 365 to 460 Kg/m2
Chemical Properties of Sandstone
Constitutent Percentages
Silica (SiO2) 93-94%
Alumina (Al2O3) 1.4-1.5%
Iron (Fe2O3) 1.5-1.6%
Lime (CaO) 0.8-0.9%
Soda (N2O) & Potash (KrO) 1.0-1.2%
Magnesia (MgO) 0.2-0.25%
Loss of Ignition (LOI) 1.0-1.2%
They are highly resistant to acids, alkalis and thermal impact and their insolubility in acids and alkalis is about 97%
Uses of Sandstone
Sandstones are used for variety of purposes. They are mainly used in paving, roofing, flooring etc. They are also used in making beams, pillars, doors and window sills, wall facing, fence posts etc.
Sandstones are resistant to saline air, which make it perfect for exterior cladding in sea-shore buildings.
They are also acid and alkali resistant. So, they are used in chemical industry for flooring, wall-covering.
They are thermal resistant so used for making fireplaces.
Limestone
Limestone is ca alcareous sedimentary rocksformed at the bottom of lakes and seas with the accumulation of shells, bones and other calcium rich goods. It is composed of calcite (CaCO3). The organic matter upon which it settles in lakes or seas, are preserved as fossils. Over thousands and millions of years, layer after layer is built up adding weight. The heat and pressure causes chemical reaction at the bottom and the sediments turn into solid stone, the limestone.
 |
| Limestone |
A part of calcium molecules if being replaced by magnesium, it is known as magnesium lime stone or dolomite limestone.
Limestone that will take a polish are considered marbles by most people, but technically, if there are still shells visible or the structure is not crystalline, it is still a limestone.
Physical Properties of Limestone
Hardness 3 to 4 on Moh's Scale
Density 2.5 to 2.7 Kg/cm3
Compressive Strength 60-170 N/mm2
Water Absorption Less than 1%
Porosity Quite low
Weather Impact Resistant
Chemical Properties of Limestone
Constituent Percentage
Lime (CaO) 38-42%
Silica (SiO2) 15-18%
Alumina (Al2O3) 3-5%
MgO 0.5 to 3%
FeO + Fe2O3 1-1.5%
Alkalies 1-1.5%
Loss On Ignition (LOI) 30-32%
Uses of Limestone
• Flooring
• Wall cladding
• Vanity tops
• Furniture
• Cement Production
• Refining Metals
• Blackboard chalk
Comparison
Sandstone and limestone both are sedimentary rocks but sandstone is formed by the sedimentation of small grains, usually quartz (silica). The individual grains are visible and vary form small to large size. While limestone is formed by the sedimentaion of finer grains of calcarious materials. As limestone is composed of finer grains so its density is more as compared to that of sandstone, and so pores in the sandstone are more Limestone, like marble and other calcareous stones, are referred to as acid sensitive. Calcareous stones are readily dissolved in acid, while sandstone do not react with the acids. Limesotne is generally soft, and can be corroded by rainwater. Sandstone is hard as compared to limestone and less corroded by rainwater, so we find it near the rivers, lakes and in desert areas.
Sandstone is preferred for the use in metallic road construction because its hardness, compressive strength is more. It is more resistant to the weathering by rainfall and can not be corroded easily by rainwater. So, at different climatic, water and weather conditions sandstone is better construction material.
About the Author
Arslan Zulfiqar He is a student of B.Sc in Transportation Engineering at "University of Engineering and Technology, Lahore, Pakistan"