Chrysocolla

Chrysocolla is a hydrated copper silicate and often mistaken for turquoise. Chrysocolla is often darker than turquoise and can be anywhere from a 2 to a 7 on the mohs scale depending on how much silica has indurated into the material and if that silica is opal or chalcedony. 

Gem chrysocolla is over 6 on the moh scale of hardness an often has a chalcedony or opal base to it. If it is translucent its known as gem silica. When opaque its known as gem chrysocolla.