Assuming 5 carat stone with top clarity, cut and color the gemstones will rank in the following sequence for their expensiveness:
1. Ruby
2. Diamond
3. Emerald
4. Sapphire
5. Pearl
6. Garnet
7. Aquamarine
8. Chrysoprase
9. Topaz
10. Citrine / Amethyst
Beryl should not be on the list as beryl is a group which includes both Emerald and Aquamarine which has already been listed above.
The reason why Ruby is ahead of Diamond is because the most expensive stone in the world which has been sold till date is Ruby, namely Burmese Ruby which are now days very rare as those mines from which they were mined has been legally sealed.
Some other stones which should be in the list are:
1. Alexandrite
2. Lapis Lazuli
3. Tanzanite