Back to Ganoksin | FAQ | Contact

Cutting petrified black coral


My friend has a piece of petrified black coral that he brought up
from the sea in South Africa and claims is prehistoric. He’s about
to take his first cabochon class and would like to cut and polish
it into a necklace.

Is there any danger to those around him when he cuts this coral?
Sheridan in Chicago


You say the coral is petrified. Do you mean as in agatized and it
happens to be black? Has it truly changed into a quartz like
substance like is found in the Tampa Bay area of FL? If so, the
black part would have a hardness of around 7. Some of the Tampa Bay
coral is also black though it is less available than the red or
brownish. If that is the case, there is no danger that I know of and
I have been cutting petrified coral for years.

If it is simply a long buried piece of true black coral, i.e.,
antipatharian or gorgonian octocoral, it could possibly not be
petrified but would be only a hardness of about 4 to 4.5 and should
be treated as one would recent black coral which can be easily filed
with a standard file. He should wear a mask while cutting it and
wash well after his cutting session. I might say that both the
antipatharian and gorgonian octocorals are considered ‘soft’ or
’horny’ corals and are prone to decomposing soon after the animal
that covers it has died. On the other hand, if it got buried in the
mud and there was no oxygen to attack it, it just might have
remained in its protein state.

Hope that helps…cheers from Don at The Charles Belle Studio in
SOFL where black coral is our speciality and where simple elegance
IS fine jewelry! @coralnut2