In its purest form chalcedony is white but impurities of other minerals cause a wide variety of different colours.
Although the blue variety tends to be known as chalcedony, many other colours have their own unique name. When chalcedony occurs with bands it's known as agate. The apple green variety is chrysoprase, the reddish orange stone is carnelian.
This blue chalcedony stone comes from Africa. It has a smooth texture, slightly waxy lustre and is highly translucent mostly around the edge.