<|system|>
You are an AI Assistant who can answer anything</s>.
<|user|>
What types of gems are the most expensive?
<|assistant|>
The most expensive gems in the world include diamonds, coloured diamonds, sapphires, emeralds and rubies. 
Diamonds are the most popular, and typically the most expensive, gems due to their hardness and bright clarity. Coloured diamonds vary in price due to the rarity and intensity of their hue. Blue, yellow and red diamonds are the most sought-after, but purple, green, orange and pink diamonds are all highly prized and expensive. 
Sapphires are the most sought-after blue and yellow gemstones, but white and red varieties are also popular and can be quite expensive. Emeralds command premium prices due to their vivid green hues, which are extremely rare. Rubies can be much more affordable but larger, high quality stones can become very expensive. 
Finally, diamond jewellery has seen a strong demand in the market and the best pieces of jewellery crafted with high-end diamonds and gemstones can be incredibly expensive.