Analytical market data of rough Boulder Opal price per carat USD. How do we calculate this data? CLICK HERE

Boulder Opal150-250 ct70-90$2.16+$0.01$2.16$2.01Moderate
Current and historical Boulder Opal market price index:
Current price per carat by date 2016-2017.
Rough average pricing scale.

Price per carat by year end.
Physical Properties of Boulder Opal:
Chemical:SiO2 · nH2O, Composed of either Cristobalite and/or Tridymite or amorphous silica.
Cleavage:None Observed
Fracture:Irregular/Uneven, Splintery, Conchoidal
Color:Every color, black, white, and clear.
Crystal System:Amorphous
Specific Gravity:1.98 - 2.25
Hardness:5.50 - 6.50
Luster:Subvitreous, Waxy, Resinous
Refractive Index:1.37 to 1.52
Transparency:Transparent to Opaque


Australian Boulder opals are the second most valuable type of opal following Australian black opal. Boulder opals are easily distinguished by their layer of solid brown ironstone left on the back of the stone. Thin veins of colourful opal form in cracks and fissures and can display any colour of the spectrum in a dazzling play of colour.

Queensland’s southwest opal fields (Quilpie, Yowah, Eromanga) are the largest sources of boulder opals so far discovered. The fields in these areas are in sediments from the Cretaceous age (100 million years ago) and it is speculated that opals need anywhere between 1-10 million years to become an opal. Most opals were formed in deeply weathered rocks in arid regions, a during high rainfall periods, small amounts of silica were dissolved by water. As the water evaporated, the remaining silica formed the minute spheres. When these spheres were packed into tight regular formations they formed the gem quality opal that is treasured around the world today.

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