What is sand? Composition & Types of Sand

Sand is a mixture of small grains of rock and granular materials which is mainly defined by size, being finer than gravel and coarser than silt. And ranging in size from 0.06 mm to 2 mm. Particles which are larger than 0.0078125 mm but smaller than 0.0625 mm are termed silt.

Sand is made by erosion or broken pebbles and weathering of rocks, which is carried by seas or rivers. And freezing and thawing during the winter break rock up the sand will be made. Sometimes Sand on beaches can also be made by small broken-up pieces of coral, bone, and shell, which are broken up by predators and then battered by the sea, and even tiny pieces of glass from bottles discarded in the sea and other mineral materials or the bones of fishes or other oceanic animals. Sand can be also considered as a textural class of soil or soil type. A sandy soil containing more than 85 percent sand-sized particles by mass.

Composition of Sand

Sand is basically made of unconsolidated granular materials consisting of either rock fragments or mineral particles or oceanic materials. It is mainly made of silicate minerals and silicate rock granular particles.

Typically quartz is the most dominant mineral here as it possesses highly resistant properties to weather. Other common rock-forming minerals like amphiboles and micas also found in sand. Heavy minerals such as tourmaline, zircon, etc can also be present in the sand in smaller concentrations. But from a high level, most sand on the beach is made up of gray or tan quartz and feldspar.

However, the most common mineral in the sand is quartz–also known as silicon dioxide. This is formed when silicon and oxygen combine. Feldspar is the most found group of minerals on the earth’s surface and forms about 65% of the terrestrial rocks. When the wind and sea whip up on the shores, they transport these teeny-tiny granules to the beach and make up the sand with this combination.

Colors of Sand

There are some different colors is found in sand. They are-

1. White Sand: It’s made of eroded limestone and may contain coral and shell fragments, in addition to other organic or organically derived fragmental material is may find in this color of sand. Magnetite, Chlorite, Glauconite, or Gypsum is also found.
2. Black Sand: Black sand is composed of volcanic minerals and lava fragments and Coral deposits. 
3. Pink Sand: Foraminifera, a microscopic organism that has a reddish-pink shell, is responsible for all this color. Coral, shells, and calcium are also found in this mix. 
4. Red-orange Color: This color is formed due to the coating of iron oxide. 
5. White-grey Color: This sand consists of fine rounded grains and It is well graded.
6. Light-brown Color: It consists of rounded grains.

Different Types of Sand

It is not possible to classify the sand. Because there is no such thing as an official sand classification. Sand is a highly variable substance and therefore it is possible to make an attempt to classify it into separate categories.

1. Coral Sand: Coral sand has several meanings.
2. Glass Sand: This type of sand mainly consists of silicon dioxide. and this is the main element in this type of sand.
3. Immature Sand: Sand composed of the same minerals that made up its parent rocks. 
4. Gypsum Sand: This type of same mainly consists of Calcium sulfate dihydrate. (CaSO₄·2H₂O)
5. Ooid Sand: Ooids are rounded pellets, and are also spheroidal coated sedimentary grains. And this type of sand is formed by calcium carbonate.
6. Silica Sand: Silica sand is almost pure quartz. 
7. Pit Sand: 

   - Obtained by forming pits into the soil

   - It is sharp, angular, porous and free from harmful salts

   - Clay & other impurities should be washed and screened before using engineering purposes.

   - Fine pit sand, when rubbed between fingers, should not leave any stain on it. It indicates the presence of clay.

   -Used for the mortars

8. River Sand: 

   - Found at river beds and banks.

   - Fine, round and polished due to rubbing action of water currents.

   - Has less frictional strength because of roundness.

   - Almost white in color.

   - Grains are smaller than pit sand, and hence more suitable for plastering work.

   - Normally available in pure condition and hence can be used for all kinds of Civil Engineering works.

9. Sea Sand:

   - Obtained from seashores.

   - Fine, rounded, and polished due to rubbing action of water.

   - Light brown in color.

   - Worst of the three types of sand because of containing a lot of salts.

   - Salts absorb moisture from the atmosphere and cause permanent dampness and efflorescence in the structure.

   - Sea salt also retards the setting action of cement.

   - Besides, it contains shells and organic matter which decompose in the body of mortar and concrete and hence reduce their life and strength.

   - Sea sand should as far as possible be discarded

10. Green Sand: Have some greenish materials. 
11. Desert Sand: Which is found in the various desert. 
12. Lithic Sand: Sometimes sand is composed of tiny rocks or comparatively more little, from this its formation its name is lithic sand.
13. Mixed Carbonate-silicate Sand: Some sand samples are a mixture of organic and inorganic sand grains. 
14. Biogenic Sand: Sand may be composed entirely of tiny skeletons — seashells, corals, forams, etc. 
15. Garnet Sand: Garnet is a common mineral in the sand but sometimes it forms the majority of it. 
16. Olivine Sand: This type of sand is very unstable. And it is mainly used for steel casting sectors. But, it is a common sand mineral in some area and sometimes makes up a major part of the sand.
17. Volcanic Sand: Volcanically affected regions have their own type of dark-colored sand with a different type of characteristics. And sometimes coal is found in that.
18. Heavy Mineral Sand: In this type of sand there are some high mass molecule is found and can make a stable structure.
19. Sands with Hematitic Pigment: Hematite is the mineral that provides reddish pigment and sandstone.
20. Continental Sand: This sand is a common whole over the world for the formation of various structures.
21. Quartz Sand: Quartz is the same as silicon sand. Mainly quartz or silicon-dioxide is the main element to form this sand.

Depending on the particle grain size, the sand is divided into four classes:

1. Very coarse
2. Coarse 
3. Medium 
4. Fine-grained

Classification of Sand According to Size (ASTM)

1. Fine Sand: All the sand particles should pass through No. 16 sieve. This is usually used in plastering works.
2. Moderately Coarse Sand: All the sand particles should pass through No. 8 sieve. This type of sand is generally used for mortar and masonry works.
3. Coarse Sand: All the particles should pass through No. 4 sieve. This type of sand is very suited for concrete work.