It’s very hard to advise about opal cutting. It’s been pointed out
that precious opal is among the easiest of gems to fashion and polish
because of its relative softness and adaptability to lapidary
techniques. True, but that’s not the whole story.
Judging rough to determine whether it’s even worth cutting, or
determining how the best stones can be made from it are matters,
where experience and judgment come in. It all depends on the type
and source of precious opal – there are many – and how the color
lies; whether the play of color is directional, whether it’s
"skin-to-skin" or thin color bars that can be oriented and cut, among
many other things. Possibly there are sand, “cotton” and other
inclusions and subsurface cracks to consider.
I recommend you locate someone with experience in these matters to
advise you, possibly through a local gem and mineral club. Precious
opal can be valuable and is a rapidly diminishing resource. Take