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
Shades of red purple. The color "rusty red" is displayed at right. "Rusty red" is a color formulated by Crayola in 1990 as one of the colors in its Silver Swirls specialty box of metallic colors. It is a metallic color. "Fire engine red" is an intense, bright red commonly used on emergency vehicles; mostly on fire engines, other associated fire service vehicles, and ambulances. "Cardinal red", also called "cardinal", is a vivid red, which gets its name from the cassocks worn by cardinals. The family of birds takes its name from the color. "Chili red" is the color of red chili peppers.