Yes, Welcome to the Board, Dude!
Thanks for the pictures you added to Natures Gifts. I love the twisted tree, but I guess that's just twisted me.
Your first question is a tough one. I had to look it up and apparently there could be more than one answer.
I agree with The Gilbey, apparently the older name for kogolong is cachalong or cacholong, and was most commonly common non-precious opal.
Names used for marketing stones can be confusing to someone trying to learn what they are, and I believe kogolong and cachalong are both marketing names.
A pure white stone would be easy to use substitutes, and create synthetically.
I'm not sure where the "volcanic" description comes from as opal, flint,chalcedony or agate, novaculite, and howlite are all sedimentary rocks.
The general consensus seems to be that kogolong is common opal, first choice, or chalcedony, second choice.
Oh yes, I did read one reference that said the kogolong could be a very rare type of "organic" opal called Tabasheer opal sometimes called Pearl Opal. But I don't know how you would be able to tell by looking at it.
Hope this helps some.
Joe