Diamonds, rubies, sapphires, and emeralds are all considered to be precious gemstones, whereas most other types of gemstones (quartz, tiger’s eye, agate, etc.) are filed under the semi-precious category. The reason that diamonds, rubies, sapphires, and emeralds are so prized is largely because they are rare, whereas most semi-precious gemstones are relatively common by comparison. The rarer a gemstone is, the more expensive it tends to be. What are the most valuable gems in the world according to both rarity and price?

The pyramids of ancient Egypt have rendered observers awestruck from the day the royal tombs first rose from the desert floor. Thousands of years ago, people were just as dumbfounded by their visual impact as we are today, and just as prone to mythologizing their origins. The astonishingly prescient achievement of the pyramids has fueled speculationthe geometrical structures must have been made by an alien species or perhaps a race of giants.

All of us have been on roads at one time or another that scared us. Maybe it was the steep drop-off along the road side, or perhaps it was all those signs warning you that a rockslide was possible at any moment. Perhaps it was a lot of sharp twists and turns, low visibility, a steep grade, or bad weather. Maybe it was just the other drivers who scared you. But it probably got you to wonder—were you driving on one of the world’s most dangerous roads?