Corundum is the scientific word for sapphire crystals. A sapphire (corundum) is an aluminum oxide mineral (Al2O3). It has a hexagonal crystal structure. Sapphire's most common color is blue, but it also can be red or green depending on its origin. The name "sapphire" comes from the Greek word for indigo, because of its color. Sapphires are often used as gemstones. They are hard and transparent or translucent. They tend to be brittle and have limited ability to change shape. However, modern technology has improved their quality and variety of shapes that can be produced. Sapphires are used in jewelry for their beautiful color and sparkling effect. Sapphires are found in several different locations around the world. India is the largest producer followed by China, Russia, and America. Each region has its own unique qualities that help determine what kinds of sapphires are available. For example, Indian sapphires tend to be softer than those mined in other places so they're good options for jewelry. The best sapphires are extremely rare. Only about 3% of mined stones meet high quality standards. The others contain some level of impurity and are not considered sapphires at all.