The material that JTclockman showed was made by Mazzucchelli 1849 and was officially called cebloplast,they called it chopped block manufacturing. The company is still on business and is still making their cebloplast materials, I still have 3 full rods of the serpent, at least that's the name attached to it here. It is an extremely difficult material to turn, I turned the two pens I've made so far by cooling the drill hole with DNA since it tends to cool faster than water, I wish I had the stones to try and thread it.
The real conundrum is it is extremely heat sensitive and soft, yet it is so brittle, it's amazing to me Brian got it to thread, there was another variety called cracked ice that was available for a while, from penmakers.com, but I don't know if they are still in business, The material on Brians pen is gorgeous, I sure would like to have some to play with.