You should be able to find O'Leary quite readily on one of the old
book s ites like www.alibris.com. He goes rather deeply into the
pattern issue. Some excellent photos of rare patterns. Most
professionals, especially Australians don't think much of his book.
Wollaston is very difficult t o find and expensive. Loenick is short
but very good. There are also a few beautiful picture books
published in Australia, one by Len Cram, that you should be able to
find in Books in Print at your local bookshop.
There are several interesting articles in Gems & Gemology including
my ow n; "Queensland Boulder Opal", Wise, R. W., Spring, 1993. "Opal
from Shew a province, Ethiopia", Johnson, et. al. Summer 1996 and a
couple of other s you will have to look up.
Don't know where your specific interest lie, but this should help.