This question was not very popular. Candidate were only able to attempt 11 (b) “write explanatory notes on gemstones”. The question requested the candidates to give the following points:

(a) Definition of gangue
The worthless minerals associated with valuable minerals in an ore or mineral deposit.

(b) Explanatory note on gemstone

• A gemstone, or gem for short, is a naturally occurring mineral desirable for its beauty, valuable in its rarity, and sufficiently durable to give lasting pleasure.
• A gemstone or gem (also called a precious or semi-precious stone, a fine gem, or jewel) is a piece of mineral, which, when cut and polished, the beauty is enhanced and may be used to make jewellery or other adornments.
• A fine coloured gemstone is hard to come by, and to get one that satisfies all criteria is harder still.        
• Coloured gemstones are miracles of nature and also very rare. They not only give you lasting value but also colour up your life!
• These commodities command high cash value especially if they are rare. Those that are hard enough to be cut and polished so that their beauty is enhanced are called gemstones.
• A gemstone therefore, is a mineral or rock whose beauty is enhanced after cutting and polishing.
• In earlier times there were no such things as synthetic gemstones but today synthetic gemstones are quite common.
• Gemstones are diverse in their beauty and many are available in a stunning variety of colours.
• Most gemstones have little beauty in the rough state. They may look like ordinary rocks or pebbles.
• After a skilled cutting and polishing of a gemstone, full colour and lustre can be seen.
• Because of the delicate nature of gemstones, their extraction from the earth’s crust demands special skills.

(c) Some metallic minerals and their main metals

1. Haematite (Fe2O3), ……. Iron. (Fe)
2. Magnetite (Fe3O4),…… Iron. (Fe)
3. Pyrite (FeS2), ……… Lead (Pb)
4. Chalcopyrite (CuFeS2);….. Lead (Pb)
5. Galena (PbS)…….. Lead (Pb); Tin (Sn) from its mineral
6. Cassiterite (SnO2)……. Tin (Sn) from
7. Bauxite (Al2O3)……  Aluminium (Al)
8. Rutile (TiO2)…………. Titanium (Ti)
9. Sphalerite (ZnS) …… Zinc (Zn)
10. Chalcopyrite (CuFeS2)……. Copper (Cu)
11. Chalcocite (Cu2S)…………… Copper (Cu)
12. Covellite (CuS) ……………… Copper (Cu)
13. Argentite (Ag2S) ………. Silver (Ag)