And it’s now missing, thanks to thieves who stole it from a private collection. Reader Ant called it to my attention from a post on ZME Science‘s “Fossil Friday”:
It’s the fossil of a giant ammonite, an ancient and prolific group of mollusks that has gone extinct without leaving descendants.
I have one (not opalized!) about a foot wide, polished and encased in its stone matrix, but this one is far better. For it’s become opalized: the mineral matrix that replaced the animal was a form of hydrated silica—the type that makes what is in my view the world’s most beautiful gem, the opal.
And what better combination than to have a fossil in opal! You can buy smaller ones on Etsy, but not like this one, said to be worth half a million dollars (or was worth, since it’s now missing):
As the website says, stuff like this is best put in a museum where it’s less liable to be stolen, and can be enjoyed by everyone. Still, I wouldn’t mind having a small version!
You can see more opalized ammonites here.