Amber

 Source: Baltic Sea Region and the Dominican Republic

Chemical: Fossilized resin

Formation: Sedimentary deposits of ancient coniferous trees. Amber is the fossilized resin of these tress and is often found to contain small plants and insects from the periods of Jurassic to Cretaceus. Amber should not be confused with copal resin which has essentially the same source but is no where near as old as amber, and is therefore not as hardened or long wearing.

Crystal System: None. Organic

Unusual Properties: Amber with identifiable insects and plants are quite rare and valuable. However, care should be take when buying expensive amber pieces with insects or plants inside. There are numerous reports of amber being heated and softened, and these items being pushed inside an amber piece by the bad guys.

Colors: Light yellow, green, dark reddish orange, and many variations of these as well.

Wearability: Will be damaged by jeweler's torch. Will burn/melt if subjected to heat. Amber has been into many different types of jewelry items for centuries.

An amber orchestra...

And a wonderful slide view of an ancient fly captured by amber.