Question

In International Union of Soil Science classification system, fine sand has a size range of:

• A. 0.2-2.0 mm
• B. 0.02-0.2 mm
• C. 0.002-0.02 mm
• D. $<$0.002 mm

Hint:

To remember the IUSS (Atterberg) system limits, think of a repeating decimal factor of 10:
Clay: $< 0.002 \text{ mm}$
Silt: $0.002 - 0.02 \text{ mm}$
Fine Sand: $0.02 - 0.2 \text{ mm}$
Coarse Sand: $0.2 - 2.0 \text{ mm}$

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Soil texture refers to the relative proportions of sand, silt, and clay-sized particles in a soil mass.
To standardize the description of these mineral particles, various soil classification systems have established specific size limits for each fraction.
Two of the most widely recognized international standards are the International Union of Soil Science (IUSS) system (historically known as the Atterberg system) and the United States Department of Agriculture (USDA) system.
These classification systems group soil separates based on their physical, chemical, and hydrological behaviors, which are heavily influenced by the effective surface area of the particles.

Step 2: Detailed Explanation:
The International Union of Soil Science (IUSS) classification scheme is based on decimal divisions established by Albert Atterberg.
Under the IUSS system, the soil separates are strictly classified as follows:
1. Coarse Sand: This fraction contains particles with diameters ranging from $0.2 \text{ mm}$ to $2.0 \text{ mm}$.
These particles are highly permeable, have low specific surface area, and exhibit negligible chemical reactivity.
2. Fine Sand: This fraction contains particles with diameters ranging from $0.02 \text{ mm}$ to $0.2 \text{ mm}$.
This is the specific range asked in the question.
3. Silt: This fraction consists of particles with diameters ranging from $0.002 \text{ mm}$ to $0.02 \text{ mm}$.
Silt particles are intermediate in size and exhibit moderate water retention properties.
4. Clay: This fraction consists of all particles with diameters less than $0.002 \text{ mm}$ (or $<2 \ \mu\text{m}$).
Clay is the highly active colloidal fraction of the soil, responsible for cation exchange capacity, plasticity, and water-holding capacity.
In contrast, the USDA system classifies fine sand slightly differently, placing it in the range of $0.10 \text{ mm}$ to $0.25 \text{ mm}$, and introduces additional subdivisions such as very coarse, coarse, medium, fine, and very fine sand.
The option (C) in the question ($0.002\text{-}0.02 \text{ mm}$) corresponds to the silt fraction under the IUSS system, and option (D) ($<0.002 \text{ mm}$) represents the clay fraction.

Step 3: Final Answer:
Thus, under the International Union of Soil Science (IUSS) standard, the particle size range for fine sand is $0.02\text{-}0.2 \text{ mm}$.