I bought the rough material at a "Rock Gem 'n' Bead" show and polished it at the Scottish Mineral & Lapidary Club in Edinburgh.
It's likely from Argentina, but I can't be sure. Below is the chunk I bought, before the sphere was cut out of the right side.
It was relatively quick to polish given its softness on the Mohs scale (3.5-4).
There was however slight undercutting due to the banding in the material. This required quite a while on the finer grade grits to really bring it down it down before the polish.
The cleaved crystal structure also posed a threat to parts flaking off. I had an issue with this in the initial shaping, but it managed to hold together beyond that.
A Minifigure for scale.