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
Heliotrope (mineral) to several magical properties, which were attributed to it from Late Antiquity. Pliny the Elder (1st century) mentioned first that the magicians used it as a stone of invisibility. Damigeron (4th century) wrote about its property to make rain, solar eclipse and its special virtue in divination and preserving health and youth. Heliotrope features as an invisibility stone in one of Boccaccio's stories in the "Decameron" and as a healing magic item in a musical comedy derived from it. Heliotrope is sometimes used in carved signet rings and is the traditional birthstone for March. The primary source of the stone