Well… having looked up the site: it tells us it being a fossil. The vendor himself does not mention the place of origin ( or must have overlooked it completely?). No details as to determine it actually is a confirmed fossil…
Knowing opal settles in voids from the outside in, might not be deformed as much as thought it is, would it have been an oyster or something similar. I would say the opal might have filled the void in 2 stages (3 even?): the first being filling just part with common opal and then gem opal moved in. Any claim as to organic matter being opalized I would say is highly questionable, because it is the first to disappear. There are loads of non-fossil opals having the same features, so I would say: artefact. What ís clear is that the entire outline is different, so: yes, fossil. Not an expert in what species.
The matrix: not to be removed or not removed as a whole. It refers to the field of origin and removel might damage the specimen. Ask an fossil expert what to do and do nót try doing it yourself, it being rare. Can only destroy it one time.
And well… as for the price… without any detail about what we have discussed above nor giving details that apparently áre available, no certified verification either… the vendor comes up with a price of… 924,000.00
It is in the details, confirmed.