Which two minerals are the most commonly cited gem species?

• A. Diamond and Onyx
• B. Emerald and Ruby
• C. Chalcedony and Quartz
• D. Opal and Jasper

Answer: (C)

Gem materials are often grouped by mineral species, and two of the most frequently named ones are quartz and chalcedony. Quartz is the most common gemstone mineral and includes a wide range of color varieties that are widely used in jewelry—amethyst, citrine, smoky quartz, rose quartz, and more. Chalcedony, while crystallographically distinct in appearance, is a cryptocrystalline form of silica and yields many well-known stones such as agate, carnelian, onyx, chrysoprase, and jasper. Because chalcedony covers a broad set of visually different stones and quartz covers a huge spectrum of color and clarity, together they represent an enormous breadth of widely used gem materials, making them the most commonly cited gem species. The other options pair minerals that are iconic but do not together span as broad a range of commonly used gemstone materials, and in some cases jasper is itself a chalcedony variety, or onyx is a chalcedony form, which narrows the scope compared to the quartz–chalcedony pairing.