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
Mineral evolution of mineral species. However, mineral extinction is not truly irreversible; a lost mineral could emerge again if suitable environmental conditions were re-established. In the early Universe, there were no minerals because the only elements available were hydrogen, helium and trace amounts of lithium. Mineral formation became possible after heavier elements, including carbon, oxygen, silicon and nitrogen, were synthesized in stars. In the expanding atmospheres of red giants and the ejecta from supernovae, microscopic minerals formed at temperatures above 1500 degrees Celsius (°C). Evidence of these minerals can be found in interstellar grains incorporated into primitive meteorites called chondrites, which are