Question

Which of the following is NOT a clay minerals?

• A. Organic colloids
• B. Chlorite
• C. Illite
• D. Apatite

Hint:

Remember that clay minerals are secondary minerals (e.g., Kaolinite, Illite, Smectite, Chlorite).
Apatite, Quartz, and Feldspars are primary minerals.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Soil mineralogy classifies minerals into primary minerals (crystallized from magma) and secondary minerals (formed by weathering of primary minerals, including clay minerals).

Step 2: Detailed Explanation:
- Illite and Chlorite are secondary aluminosilicate clay minerals belonging to the phyllosilicates class.
- Organic colloids (humus) are part of the soil colloidal fraction (alongside clay).
- Apatite is a primary phosphate mineral (calcium phosphate).
It is not a clay mineral, but rather serves as a primary source of phosphorus in soils.

Step 3: Final Answer:
Apatite is NOT a clay mineral, making option (D) the correct choice.