Sample with smooth black rocks inside it.

[Mexico]

The black parts are slick and easy to carve into ( but still hard). The rest is like a normal rock. This is a small piece from were I found it here in Mexico. There is more but its pick and hammer time to get it. So I just knocked off this sample. It my be Onyx but i'm not sure. The size of this sample is about 4'' x 3''

P.S. I posted in the Gem. section also. but this section seems to get more persons helping me with these items.

Any help will be awesome. Cheers