Fossil ivory is the only source of legal ivory used in trade worldwide and there are only two sources of it namely mammoth ivory and ancient walrus ivory. Though mammoth ivory is excavated in the tundra regions of Arctic and Siberia, fossil walrus ivory is excavated from the village sites of Eskimo and is usually dated to be 200 to 2000 years old.
There are various hues in the fossil ivory ranging from black streaks to orange and brown shades. The colored ivory depends on soil minerals that lead to the streaking. Ivory buried in iron rich soil has a rust orange and brown shade while natural dark colored soil leads to a range of shades from grey to black in the ivory.
Ancient Eskimo used a lot of ivory from excavated mammoth tusks to walrus ivory due to the lack of trees in the region. Today all of this ivory is expensive but they used it for the holding up their tents, as skis and more. Another aspect of fossil ivory is beach ivory. Old walrus ivory is known to be collected from beaches as walrus perished in the seas or were harvested from the ancient Eskimo villages that are now below the ocean and wash up the shores after storms.
Some of the beach ivory has higher mineralization due to the constant contact with salt water and are fossilized more, making it harder and easier to carve than fresh ivory. However, artists prefer less stress on ivory irrespective of whether it is mammoth tusks or walrus ivory. If you are looking to invest in high quality mammoth tusk ivory, check out a range of collectible art pieces at http://www.mammothivory.info