Ruby: The King of Gemstones _ This bright red gemstone is one of the best known gemstones in the world. Natural rubies are quite rare and expensive. Larger transparent rubies are exceptionally rare, far more rare than diamonds. Some rubies have a slight blue hue to them - these precious gemstones fetch the highest price. Rubies have always played an important role in the gemstone world. They were used to decorate crowns, armor and jewelry of nobility.