Note the distinct demarcation between the inner and outer dentine, and the outwardly radiating lines.

https://www.fws.gov/lab/ivory_natural.php#walrus

The dentine is composed of two types: primary dentine and secondary dentine (often called osteodentine). Primary dentine has a classical ivory appearance. Secondary dentine looks marble or oatmeal-like. This type of secondary dentine is diagnostic for walrus tusk ivory.