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 in this stage is mineral inclusions in zircon crystals, which date back as far as 4.4 Ga. Among the minerals in the inclusions are quartz, muscovite, biotite, potassium feldspar, albite, chlorite and hornblende. In a volatile-poor body such as Mercury and the Moon, the above processes give rise to about 350 mineral species. Water and other volatiles, if present, increase the total. Earth was volatile-rich, with an atmosphere composed of N, CO and water, and an ocean that became steadily more saline. Volcanism, outgassing and hydration gave rise to hydroxides, hydrates, carbonates and evaporites. For Earth, where this stage coincides