Question

Gypsum, carbonates, micas, and feldspars are primarily located in:

• A. Arid and Temperate regions
• B. Temperate and Humid regions
• C. Arid and Semi-arid regions
• D. Humid and Sub-humid regions

Hint:

Soluble minerals like gypsum and calcium carbonate are diagnostic indicators of dry climates (Arid and Semi-arid regions) where leaching is insufficient to remove them from the soil profile.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Soil mineralogy and the geographic distribution of soil minerals are heavily governed by the prevailing climate, especially precipitation and temperature.
Climate regulates the rate and intensity of chemical weathering (such as hydrolysis, hydration, and dissolution) and the leaching of soluble ions.
Highly soluble minerals and easily weatherable primary minerals only accumulate in environments where precipitation is low and evapotranspiration is high.
Conversely, in humid regions with high rainfall, highly soluble minerals are rapidly dissolved and leached down the soil profile, leaving behind highly weathered, insoluble secondary minerals.

Step 2: Detailed Explanation:
Let us analyze the chemical properties of the listed minerals and their behavior under different climates:
1. Gypsum (\(\text{CaSO}_4 \cdot 2\text{H}_2\text{O}\)) and Carbonates (\(\text{CaCO}_3\), \(\text{MgCO}_3\)):
These are relatively soluble calcium-bearing minerals.
In humid regions with high precipitation, they dissolve rapidly and are leached deep into the groundwater.
However, in Arid and Semi-arid regions, where rainfall is limited and potential evapotranspiration (PET) exceeds precipitation, leaching is minimal.
This lack of leaching leads to the accumulation of these minerals in the upper horizons, forming distinct calcic or gypsic horizons (as seen in Aridisols and some Alfisols/Mollisols).
2. Micas and Feldspars:
These are primary silicate minerals that are abundant in the Earth's crust.
They are highly susceptible to chemical weathering (especially hydrolysis).
In humid and sub-humid tropical climates, micas and feldspars weather rapidly to form secondary clay minerals like kaolinite or iron and aluminum oxides.
In contrast, in arid and semi-arid regions, the low moisture availability slows down chemical weathering rates, allowing these primary minerals to persist in the soil sand and silt fractions.
Therefore, these minerals are primarily located and preserved in Arid and Semi-arid regions.
This corresponds to option (C) in the classification.

Step 3: Final Answer:
Thus, the geographical regions where gypsum, carbonates, micas, and feldspars are primarily located are Arid and Semi-arid regions.