The lovely dark sea green oval seraphinite gemstone cabochon shown here is 20mm long.
The word seraphim refers to angels, and seraphinite is supposed to have gotten its name due to its resemblance to feathers. Seraphinite is mined in a limited area of eastern Siberia in Russia. It was originally known as green chlorite.
Seraphinite is believed to promote self healing and aid with contacting the spirit world.
I used this cabochon to create this custom piece: