One of the most unusual material used to make go stones is ivory. I found a nice picture of such a stone. Notice the interesting pattern in the white stone. It’s very different from white stones made from clamshells.
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Found some pictures of a beautiful set of ivory go stones in mulberry go bowls from a Japanese auction.
Enjoy.
One of the mulberry bowls has the words 懐志 stamped on the bottom. The stamp seems to be the trademark of the 柴田木工所 Shibata woodworking shop in Okayama Prefecture.
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One of our dear readers, Taewook Kim, of Korea provided a nice link to pictures of the famous Mokuga Shitan no Kikyoku (木画紫檀碁局). This red sandalwood go board was a gift from China to the Japanese Emperor Shomu (701-756) and is currently housed in the Shosoin, in Nara, Japan. You can compared the lavish painted ivory stones of this set with the plainer ivory stones in the photos above. But it seems you can’t see the pattern of the ivory in the pictures of the painted stones.
http://nury.tistory.com/119
I have added another link to the official Japanese page of the Mokuga Shitan no Kikyoku.
http://shosoin.kunaicho.go.jp/shosoinPublic/top.do
Click on 遊戯具 and then on 木画紫檀碁局
Tchan001's Blog 
Very nice. How old are they?
Not sure, I only have the photo. No other info
I have a picture of ivory go stones. Send Email to ktw@hknu.ac.kr if you want the picture.