Chalcedony

I was interested in the gemstone chalcedony and thought I would do some research.

Chalcedony is also known as agate. Its colors are bluish white, or gray. The various types differ in color due to metallic impurities, such as iron, nickel, copper, and titanium, present during crystallization.

Some of the best known chalcedony species are:

Bloodstone, an opaque, dark green chalcedony with red spots (caused by iron oxide).

Blue chalcedony, called "Mohave" and "Mt. Airy Blues", originating in California and Nevada, are slightly to moderately grayish blue with a light to medium color range.
Blue chalcedony from Namibia, often called "African Blue", varies from grayish to nearly pure blue and from light to medium dark. The most unusual and most valuable type is from Oregon. Its blues are modified by slight to moderate amounts of pink, making a noticeably lavender gem, which nonetheless is called "Holly Blue."

Carnelian ranges in color from yellow-orange to rich, near reddish orange, to orangey brown, and varies from semi-opaque to highly translucent.

Chrysocolla, marketed as "Gem Silica" is relatively rare. It's color is blue to blue-green, opaque to near transparent material is the most expensive type of chalcedony. Its color agent is copper.

Chrysoprase, apple green chalcedony that derives its color from nickel, ranges from nearly opaque to nearly transparent. Its color spectrum includes olivey, to nearly pure greens of medium tone. Very fine, highly saturated pieces have been successfully misrepresented as Imperial jade.