Baltic Amber necklace. Baltic Amber is fossil of resin that is like sap which formed over 45millions years old from Baltic sea region of Europe. Although not a mineral, it is generally classified as a gemstone. A common misconception is that Amber is made of tree sap. Sap is the fluid that circulates through a plant's vascular system, while resin is the semi-solid amorphous organic substance secreted in pockets and canals through epithelial cells of the tree.