Chalcedony to as prase. However, the term prase is also used to describe green quartz, and to a certain extent is a color-descriptor, rather than a rigorously defined mineral variety.) Blue-colored chalcedony is sometimes referred to as "blue chrysoprase" if the color is sufficiently rich, though it derives its color from the presence of copper and is largely unrelated to nickel-bearing chrysoprase. Heliotrope is a green variety of chalcedony, containing red inclusions of iron oxide that resemble drops of blood, giving heliotrope its alternative name of bloodstone. In a similar variety, the spots are yellow instead, known as plasma. Moss agate
Birthstone American Gem Trade Association and Jewelers of America added spinel as an additional birthstone for August. Britain's National Association of Goldsmiths created their own standardized list of birthstones in 1937. Eastern cultures recognize a similar range of gemstones associated with birth, though rather than associating a gem with a birth month, gemstones are associated with celestial bodies, and astrology is employed to determine the gemstones most closely associated with and beneficial to a particular individual. For example, in Hinduism there are nine gemstones associated with the "Navagraha" (celestial forces including the planets, the sun, and the moon), known in Sanskrit