Which one of the following pairs of principal chemical constituents in water and their source is correct ?
Ca : Amphiboles, Feldspars, Gypsum
NO₃ : Apatite, Fluorite, Mica
CO₃ : Feldspars, Clay minerals
F : Dolomite, Gypsum, Anhydrite
Answer is Right!
Answer is Wrong!
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UPSC Geoscientist – 2024
– **Nitrate (NO₃⁻):** Nitrates are anions usually derived from the nitrogen cycle, including decomposition of organic matter, agricultural fertilizers, and sewage. While nitrogen is present in some minerals (e.g., saltpeter), the significant source of nitrates in water is typically biogeochemical processes and human activities, not the mineral types listed (Apatite – phosphate, Fluorite – fluoride, Mica – silicate). Option B is incorrect.
– **Carbonate (CO₃²⁻):** Carbonates are derived from the dissolution of carbonate rocks like limestone (primarily CaCO₃) and dolomite (CaMg(CO₃)₂). While weathering of silicate minerals like feldspars contributes to alkalinity and the formation of bicarbonate (HCO₃⁻) or carbonate, feldspars and clay minerals themselves are not primary sources of the carbonate ion in the same way carbonate rocks are. Option C is incorrect.
– **Fluoride (F⁻):** Fluoride in natural water often comes from the dissolution of fluoride-bearing minerals like Fluorite (CaF₂), cryolite (Na₃AlF₆), and some micas and apatites. Dolomite, Gypsum, and Anhydrite are calcium/magnesium carbonates or sulfates and are not primary sources of fluoride. Option D is incorrect.