Question

Arrange the minerals based on the descending order of weatherability
(A) Biotite $>$ Augite $>$ Garnet $>$ Quartz
(B) Zircon $>$ Tourmaline $>$ Olivine $>$ Muscovite
(C) Albite $>$ Ilmenite $>$ Hornblende $>$ Olivine
(D) Anorthite $>$ apatite $>$ Zircon $>$ Titanite

• A. Only (A)
• B. (A) and (B)
• C. (A), (B) and (C)
• D. (A), (B), (C) and (D)

Hint:

Remember Goldich's Weathering Series: Minerals formed at the highest temperatures (like Olivine and Pyroxenes) are the most unstable at Earth's surface and weather first, while Quartz is the most stable and resistant to weathering.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Mineral weatherability refers to the ease with which a mineral undergoes physical and chemical breakdown under environmental conditions.
The Goldich Weathering Series ranks common rock-forming minerals based on their stability and rate of weathering.

Step 3: Detailed Explanation:
Let us analyze Goldich's stability series for minerals:
- Minerals that crystallize at high temperatures (like olivine and pyroxenes) are chemically unstable at surface conditions and weather rapidly.
- Minerals that crystallize at lower temperatures (like muscovite and quartz) are highly stable and weather very slowly.
- The order of increasing stability (decreasing weatherability) of common minerals is:
\[ \text{Olivine} < \text{Augite (Pyroxene)} < \text{Hornblende (Amphibole)} < \text{Biotite} < \text{K-Feldspar} < \text{Muscovite} < \text{Quartz} \]
- Let us analyze Sequence (A) in terms of weatherability (ease of breakdown):
Biotite has higher weatherability than highly stable minerals like Garnet and Quartz.
Augite (pyroxene) is highly unstable and has a higher weatherability than Biotite.
Garnet is a highly resistant metamorphic mineral, and Quartz is the most resistant mineral in the series.
Thus, the descending order of weatherability (from most weatherable to most stable/least weatherable) is correctly represented in Sequence (A) as:
\[ \text{Biotite} > \text{Augite} > \text{Garnet} > \text{Quartz} \]
- Let us evaluate why other options are incorrect:
- Sequence (B): Places highly stable minerals like Zircon and Tourmaline as the most weatherable, which is incorrect because they are extremely resistant to weathering.
- Sequence (C): Places Albite (feldspar) as more weatherable than Olivine, which is incorrect because Olivine is much more unstable and weathers faster than feldspars.
Therefore, only sequence (A) is correct.

Step 4: Final Answer:
The correct descending order of weatherability is represented only by sequence (A).