Australian Boulder Opal
Natural Australian boulder opal is Queensland’s signature gemstone, formed millions of years ago when silica rich water filled cracks inside host ironstone boulders. Because the natural host rock is left on the back during cutting, boulder opal is durable and displays a vibrant play of color against a dark, earthy base. This collection showcases authentic, untreated solid boulder opals sourced directly from famous fields such as Winton and Koroit.
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92.35ct Natural Koroit Boulder Opal Large Teardrop
US$330Type: Natural Solid Untreated Boulder Opal
Origin: Koroit, Queensland, Australia
Dimensions: 40 x 28 x 10 mm approx
Weight: 92.35ct approx
Color: Orange blue fire in natural boulder opal
Use: Ideal for custom opal ring, pendant, or fine jewelry
Aqua Blue Queensland Boulder Opal Teardrop Ringstone 3.7 ct
US$325Natural Solid Untreated Australian Boulder Opal Polished Stone
Weight: 3.7 carats
Dimensions: 13x10x3.5 mm
Source: Winton, QLD, Australia
Size and weight are approximate
3.4ct Natural Boulder Opal Deep Blue Fire
US$320100% Natural Solid Boulder Opal Polished Stone
Weight: 3.4 ct
Dimensions: 14.8×8.2×3 mm
Source: Winton,QLD, Australia
Size and weight are approximate
Blue Winton Boulder Opal 5 ct
US$320Natural Solid Untreated Boulder Opal Polished Stone
Weight: 5 carats
Dimensions: 16.5×8.5×3.2 mm
Source: Winton, QLD, Australia
Size and weight are approximate
3.91ct Natural Boulder Opal Blue Fire
US$300100% Natural Solid Boulder Opal Polished Stone
Weight: 3.91 ct
Dimensions: 16.5×6.5×3.5 mm
Source: Winton,QLD, Australia
Size and weight are approximate
26.81ct Double Sided Vein Australian Koroit Boulder Opal
US$290100% Natural Polished Boulder Opal
Weight: 26.81 ct
Dimensions: 46.5×12.5×4.5 mm
Source: Koroit, QLD, Australia
5.85ct Natural Boulder Opal
US$285100% Natural Solid Boulder Opal Polished Stone
Weight: 5.85 ct
Dimensions: 15.5x11x3 mm
Source: Winton,QLD, Australia
Size and weight are approximate
15.28ct Natural Boulder Opal Blue Green
US$285100% Natural Polished Boulder Opal
Weight: 15.28 ct
Dimensions: 38x15x4.5 mm
Source: Winton,QLD, Australia
10ct Boulder Opal Red Blue Green Stripe Flash
US$28010ct Australian boulder opal from Winton Queensland reveals striking red, blue, and green stripe flashes across its dark ironstone body. Expertly polished freeform cut, 100% natural and untreated. Ideal for fine jewelry, collector gemstone, or meaningful October birthstone gift.
Type: Natural Solid Boulder Opal
Origin: Winton, Queensland, Australia
Dimensions: 24 x 12.5 x 4 mm (approx.)
Weight: 10ct (approx.)
Color: Brilliant red, blue, and green stripe flash
Cut/Shape: Freeform polished cabochon
Treatment: 100% natural, untreated opal (not a doublet or triplet)
Purple Striped Boulder Opal 28.1 ct
US$275Natural Solid Untreated Australian Boulder Opal Polished Stone
Weight: 28.1 carat
Dimensions: 27×19×5.5 mm
Source: Winton, QLD, Australia
39.17ct Double Sided Koroit Boulder Opal
US$270100% Natural Polished Boulder Opal
Weight: 39.17 ct
Dimensions: 32x23x7 mm
Source: Koroit,QLD, Australia
78.76ct Large Boulder Opal Teardrop Veins
US$270100% Natural Polished Boulder Opal
Weight: 78.76 ct
Dimensions: 45.5×22.5×8 mm
Source: Koroit,QLD, Australia
7.52ct Natural Boulder Opal Blue Fire
US$255100% Natural Solid Boulder Opal Polished Stone
Weight: 7.52 ct
Dimensions: 12×12.5×5.5 mm
Source: Winton,QLD, Australia
Size and weight are approximate
18.44ct Natural Boulder Opal Deep Purple Fire
US$250100% Natural Boulder Opal
Weight: 18.44 ct
Dimensions: 28x15x5 mm
Source: Winton, QLD, Australia
2.41 ct Natural Turquoise Green Boulder Opal
US$240💎 Opal Details:
Weight: 2.41 ct
Dimensions: 19.4x5x2.8 mm
Origin: Winton, Queensland, Australia
Size and weight are approximate
2.58 ct Natural Boulder Opal Blue Green
US$240💎 Opal Details:
Weight: 2.58 ct
Dimensions: 14.5x7x3mm
Origin: Winton, Queensland, Australia
Size and weight are approximate
Polished Green Blue Boulder Opal 2.73 ct
US$240💎 Opal Details:
Weight: 1.18 ct
Dimensions: 10×5.5×2.2 mm
Origin: Winton, Queensland, Australia
Size and weight are approximate
2.18 ct Natural Boulder Opal
US$240Weight: 2.18 ct
Dimensions: 13 x 6 x 2.7 mm
Origin: Winton, Queensland, Australia
Size and weight are approximate
Green Flash Natural Boulder Opal 2.38 ct
US$235💎 Opal Details:
Weight: 2.38 ct
Dimensions: 14×6.7×2.7 mm
Origin: Winton, Queensland, Australia
Size and weight are approximate
Blue Green Solid Boulder Opal 1.05 ct
US$235💎 Opal Details:
Weight: 1.05 ct
Dimensions: 12×4.8×2 mm
Origin: Winton, Queensland, Australia
Size and weight are approximate
Natural Australian Solid Boulder Opal 1.83 ct
US$235💎 Opal Details:
Weight: 1.83 ct
Dimensions: 11.5×5.2×2.8 mm
Origin: Winton, Queensland, Australia
Size and weight are approximate
34.75ct Large Natural Koroit Boulder Opal
US$227100% Natural Polished Boulder Opal
Weight: 34.75 ct
Dimensions: 38×22.5×7 mm
Source: Koroit,QLD, Australia
14.43ct Boulder Opal Purple Blue
US$220100% Natural Boulder Opal
Weight: 14.43 ct
Dimensions: 31×11.5×4.5 mm
Source: Winton, QLD, Australia
1.57ct Natural Boulder Opal
US$215100% Natural Solid Boulder Opal Polished Stone
Weight: 1.57 ct
Dimensions: 12x6x2 mm
Source: Winton,QLD, Australia
Size and weight are approximate
3.03ct Natural Boulder Opal
US$215100% Natural Solid Boulder Opal Polished Stone
Weight: 3.03 ct
Dimensions: 19×6.5×2.2 mm
Source: Winton,QLD, Australia
Size and weight are approximate
3.48ct Natural Boulder Opal Vivid Blue Green Fire
US$200💎 Opal Details:
Carat Weight: 3.48ct
Dimensions: 20 × 6 × 3 mm
Type: Natural Solid Boulder Opal
Source: Winton, QLD, Australia
Size & Weight: Approximat
4.31ct Natural Boulder Opal Vivid Blue Green
US$1654.31ct Australian boulder opal from Winton Queensland features vivid blue and green fire glimmering across its natural ironstone body. Expertly polished in a curved freeform shape, this 100% natural untreated gemstone is ideal for fine jewelry, October birthstone gifts, or collector investment.
Type: Natural Solid Boulder Opal
Origin: Winton, Queensland, Australia
Dimensions: 19 x 6 x 3 mm (approx.)
Weight: 4.31ct (approx.)
Color: Vivid blue and green fire with natural ironstone matrix
Cut/Shape: Curved freeform polished cabochon
Treatment: 100% natural, untreated opal (not a doublet or triplet)
32ct Natural Boulder Matrix Opal Koroit Australia
US$165Opal Details:
Type: Natural, Solid, Untreated Boulder Opal
Origin: Koroit, Queensland, Australia
Dimensions: 39 × 12 × 6.5 mm (approx.)
Weight: 32ct (approx.)
The Unique Character and Durability of Boulder Opal
Boulder opal is the second most valuable type of precious opal and is highly favored for its durability. The natural ironstone backing acts as a sturdy shield, giving boulder opal superior strength compared to other solid opals. Because the veins of precious opal in the boulders are very thin, lapidaries must cut the stone to follow the natural undulating lines of the color bar. This results in beautiful, organic, freeform shapes that make each gemstone entirely unique.
In this collection, buyers will find variety in styles, from Winton boulder opals displaying clean faces of rolling color to Koroit boulder opals showcasing intricate matrix veins running through the ironstone. To deepen your organic geological knowledge, explore our comprehensive boulder opals detailed guide on natural formations. Unlike composite doublets, boulder opal is a fully natural, one piece gemstone fused by nature over geological epochs. Shoppers can review details about shipping rates and options on the Opal Galaxy shipping policy page. Geological studies published by Geoscience Australia describe these formations within the Cretaceous Winton Formation of southwest Queensland.
Frequently Asked Questions
What is boulder opal?
Boulder opal is precious opal naturally fused to its brown ironstone host rock.
Where does boulder opal come from?
All natural boulder opal comes from western Queensland fields including Winton, Koroit, and Yowah.
Is the ironstone backing real?
Yes, the backing is the natural host rock and is completely organic, never artificially glued.
Is boulder opal durable?
Boulder opal is the most durable solid opal variety due to the supportive ironstone backing.
How is boulder opal valued?
Value depends on face color brilliance, patterns, size, and minimal ironstone intrusion on the surface.