UPSC Prelims 2008 Q113: Science & Technology – Materials & Engineering

UPSC Prelims 2008, General Studies Paper I · Science & Technology

What are Rubies and Sapphires chemically known as?

Answer: (b) Aluminium oxide

Explanation

Chemical composition of Rubies and Sapphires

These precious gemstones, despite their different colours, share a common underlying mineral composition.

Option	Verdict	Reason
(a) Silicon dioxide	Incorrect	This is the composition of quartz-based gems (like amethyst), not rubies/sapphires
(b) Aluminium oxide	Correct	Rubies and Sapphires are both varieties of corundum, chemically known as Aluminium oxide, with colour differences caused by trace impurities
(c) Lead tetroxide	Incorrect	Unrelated to these gemstones
(d) Boron nitride	Incorrect	Unrelated to these gemstones

Ruby and Sapphire facts:

Point	Detail
Mineral	Corundum
Chemical formula	Aluminium oxide (Al₂O₃)
Colour cause	Trace impurities (chromium for red rubies, etc.)

Answer: (b) Aluminium oxide.

(a) Incorrect. Silicon dioxide describes quartz-based gems, not rubies/sapphires.
(b) CORRECT. Rubies and Sapphires are chemically Aluminium oxide (corundum).
(c) Incorrect. Lead tetroxide is unrelated to these gemstones.
(d) Incorrect. Boron nitride is also unrelated.

Rubies and Sapphires are both chemically Aluminium oxide (the mineral corundum), with their different colours caused by trace impurities.

Rubies and Sapphires are chemically known as Aluminium oxide.

Confusing corundum (Aluminium oxide) with quartz-based (silicon dioxide) gemstones.
Not knowing that rubies and sapphires are chemically identical, differing only in trace impurities causing colour.
Mixing up unrelated chemical compounds with these gemstones' actual composition.

Rubies and Sapphires = chemically identical (Aluminium oxide/corundum), colour differences come from trace impurities.