This rare, 30,000-year-old blue mammoth tusk was discovered in Alaska in 2017.

[u/GoldenChinchilla]

The blue coloration is believed to develop when animal remains that are low in iron but high in phosphates are buried in damp sediment that is rich in iron but poor in phosphates.

The tusk was reportedly put up for auction, although its estimated value was not disclosed.

[u/augustwest2155]

I saw in this thread that it is almost 10 ft long...the picture sure does not do justice as to how huge this is.