Opal The Phenomenal Gemstone, Extralapis English #10, used/like new.  OUT OF PRINT.  No longer being sold by publisher.  One of the most popular issues of the series, and probably the best overall reference on opals in modern times.
USED copies like this go for just under $200 right now on Amazon, WHEN you can find one.  I have seen copies go for as much as $300.  I have an extra copy which I am listing here.