CAPF AC 2020 Q26: Science & Technology – Chemistry
Which one of the following minerals is NOT a naturally occurring silicate?
- (a) Feldspar
- (b) Zeolite
- (c) Mica
- (d) Bauxite
Answer: (d) Bauxite
Explanation
Silicate minerals
How to think: a silicate must contain silicon and oxygen.
Look for the mineral known as the ore of a metal instead.
| Mineral | What it is | Silicate? |
|---|---|---|
| Feldspar | Aluminosilicate of potassium, sodium or calcium; most common mineral in the crust | Yes |
| Zeolite | Aluminosilicate with a cage structure; used to soften water | Yes |
| Mica | Sheet silicate that splits into thin layers; an insulator | Yes |
| Bauxite | Hydrated aluminium oxide; the ore of aluminium | No |
More on bauxite:
| Fact | Detail |
|---|---|
| Formula | Aluminium oxide with water |
| Metal obtained | Aluminium |
| Leading State in India | Odisha |
Answer: (d) Bauxite.
Why each option is right or wrong
- (a) Incorrect. Feldspar is a silicate and the most abundant mineral group in the crust.
- (b) Incorrect. Zeolites are aluminosilicates, used in water softening.
- (c) Incorrect. Mica is a sheet silicate, used as an electrical insulator.
- (d) CORRECT. Bauxite is an oxide ore of aluminium and contains no silicate unit.
Key point
Silicates: feldspar, zeolite, mica, quartz, asbestos. Bauxite is hydrated aluminium oxide, the ore of aluminium, not a silicate.
Remember
Bauxite = aluminium oxide ore, not a silicate.
Common mistakes
- Thinking bauxite is a silicate because clay minerals also contain aluminium.
- Not knowing that zeolites are natural minerals as well as man-made.
- Confusing oxide ores (bauxite, haematite) with silicate minerals.
Exam tip
Spot the ore: bauxite is always taught as the ore of aluminium, an oxide.
Sources
- NCERT Class XI Chemistry — The p-Block Elements (silicates and zeolites)
- NCERT Class XII Chemistry — General Principles and Processes of Isolation of Elements (ores of aluminium)