Amber

Amber (or, technically, resinite) is fossilized tree resin (not sap), which has been appreciated for its colour and natural beauty since Neolithic times. Good quality amber is used for the manufacture of ornamental objects and jewelry. There are five classes of amber, defined on the basis of their chemical constituents.

Because it originates as a soft, sticky tree resin, amber sometimes includes animal and plant material as inclusions.

Appearance
Amber occurs in a range of different colours. As well as the usual yellow-orange-brown that is associated with the colour "amber", amber itself can range from a whitish colour through a pale lemon yellow, to brown and almost black. Other more uncommon colours include red amber (sometimes known as "cherry amber"), green amber, and even blue amber, which is rare and highly sought after.

Source

 * http://en.wikipedia.org