Final answer:
A large, finished crystal of synthetic ruby is often referred to as a boule. The red color of synthetic rubies originates from Cr³+ impurities replacing Al³+ in the aluminum oxide lattice. Rubies can be used for gemstones or industrial purposes like in the production of lasers.
Step-by-step explanation:
A large, finished crystal of synthetic ruby is often called a boule. Synthetic rubies are made using methods like the flame fusion process, where fine powders of aluminum oxide and chromium are melted together to form a crystal. The red color of rubies is due to the presence of Cr³+ impurities within the crystal structure, specifically replacing some of the Al³+ ions in the crystal lattice of aluminum oxide (Al2O3).
This process forms a large, cylindrical single crystal called a boule, which can be cut into gemstones or used in various industrial applications, such as the basis of a ruby laser. In a ruby laser, the presence of chromium atoms allows for the achievement of a population inversion, which is necessary to produce laser light.
Ruby is known as an allochromatic mineral, indicating that its color arises from these trace impurities rather than from the main elements of the mineral itself. These small amounts of Cr³+ integrated into the aluminum oxide lattice give ruby its characteristic deep red color, making it a highly sought-after gemstone in both its natural and synthetic forms.