These halls contain exquisite treasures, which can be systematically arranged according to their similarities and differences in the same manner as animals and plants. In the Hall of Minerals the visitor finds minerals composed of a single element, such as gold and copper, and groups that combine several elements, such as the silicates quartz, amethyst, and mica. The Hall of Gems displays groups of stones that showcase an extraordinary range of size, color, and shape. Among these specimens is the 563-carat Star of India, the largest and most famous star sapphire in the world. Formed some two billion years ago, the Star of India was discovered several centuries ago and donated to the Museum by J. P. Morgan in 1900. Also featured in the Hall of Gems is the Patricia Emerald, a 632-carat specimen that is one of the very few large, gem-quality emeralds that have been preserved uncut. The specimen is exceedingly rare not only because of its size and color, but also because of its dihexagonal, or twelve-sided, shape.