The question was highly technical and a bit tasking. Performance of the students were fairly good. The question requested the candidates to give the following points:

Important physical and optical properties that should be considered for cutting and polishing gemstones

1. Hardness – Hardness (and durability) is considered an important characteristic of a gemstone. Regardless of how beautiful a stone may appear, for it to be suitable as a gemstone, it will need to be reasonably durable and hard. There are numerous different ways of considering hardness, but the main one for gems is their resistance to abrasion. Some minerals (such as those formed by evaporation of sea water) dissolve easily and clearly these would be poor gem materials.
2. Resistance to scratching: this is evaluated by consideration of gem hardness. There are two measures of hardness: scratch hardness and indentation hardness. Generally, we use the scratch hardness.
3. Dichroism or pleochroism – the property of appearing in different colours when viewed in different directions
4. Cleavage – Cleavage and fracture refer to the characteristic manner in which gems will break when an external force or stress is applied. Some minerals have a special way of breaking parallel along planes of atomic weakness, creating smooth flat surfaces. This break is called cleavage.
5. Fracture – Fracture is a break in a direction other than along cleavage planes and results when the bonding forces are similar in all directions.
6. Dispersion – the breaking up of white light into its constituent colours.
7. Optical phenomenon refers to the property of some minerals when exposed to light. The optical phenomena are as follows:

• Chatoyancy – Cat’s-eye-effect (for example: chrysoberyl, sapphire, ruby, and apatite)
• Asterism – Star effect (for example: sapphire, ruby, rose quartz, and garnet)
• Iridescence – Play of colour effect (for example: opal, or iolite)
• Fire – Dispersion of light (for example: diamond, demantoid and zircon)
• Stability: Stability is the gems resistance to fading or other alteration due to light, heat or chemical attack. Minerals classified as carbonates, such as malachite, pearl and rhodochrosite, may be damaged by chemical attack.

Transparency: Transparency is how we measure how clear a stone is. If a stone is perfectly clear it is transparent. If you cannot see through a stone, it is opaque. There are varying levels of transparency between these two extremes; this is known as translucent. This is important whether to cut cabochon or facet.