Oscar Heyman bracelet in platinum with 27.93 carats black opal, 10.04 carats sapphire, 9.73 carats emerald, 4.62 carats diamond, and 2.05 carats golden yellow diamond, $260,000, oscarheyman.com ...

Aside from the widely known iridescent black and white varieties, more esoteric opals include translucent orange Mexican fire opals as well as opaque Peruvian varieties in shades of pink, blue ...

For Monica Rich Kosann, whose high jewelry collection, The Jewels of Nature, uses rare Australian black and crystal opals and Mexican fire opals, the answer was hiding in plain sight.