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
USS Heliotrope (1863) as a tug and ordnance boat. She continued this duty with occasional patrols up the James River, until her transfer to the Potomac Flotilla 23 January 1865. "Heliotrope" reported for her new duties early in February, and participated 6–8 March in a joint expedition up the Rappahannock River to Fredericksburg, Virginia. In cooperation with Army units, "Heliotrope" and the other gunboats succeeded in destroying railroad facilities, a large quantity of track, and a depot of army supplies. Returning to routine patrolling in the Potomac River, she embarked with other gunboats on another expedition 16 March, sending her small boats with