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.

Filters
Add to Wishlist

92.35ct Natural Koroit Boulder Opal Large Teardrop

US$330

Type: 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

Add to Wishlist

Aqua Blue Queensland Boulder Opal Teardrop Ringstone 3.7 ct

US$325

Natural Solid Untreated Australian Boulder Opal Polished Stone
Weight: 3.7 carats
Dimensions: 13x10x3.5 mm
Source: Winton, QLD, Australia
Size and weight are approximate

Add to Wishlist

3.4ct Natural Boulder Opal Deep Blue Fire

US$320

100% 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

Add to Wishlist

Blue Winton Boulder Opal 5 ct

US$320

Natural 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

Add to Wishlist

3.91ct Natural Boulder Opal Blue Fire

US$300

100% 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

Add to Wishlist

26.81ct Double Sided Vein Australian Koroit Boulder Opal

US$290

100% Natural Polished Boulder Opal
Weight: 26.81 ct
Dimensions: 46.5×12.5×4.5 mm
Source: Koroit, QLD, Australia

Add to Wishlist

5.85ct Natural Boulder Opal

US$285

100% Natural Solid Boulder Opal Polished Stone
Weight: 5.85 ct
Dimensions: 15.5x11x3 mm
Source: Winton,QLD, Australia
Size and weight are approximate

Add to Wishlist

15.28ct Natural Boulder Opal Blue Green

US$285

100% Natural Polished Boulder Opal
Weight: 15.28 ct
Dimensions: 38x15x4.5 mm
Source: Winton,QLD, Australia

Add to Wishlist

10ct Boulder Opal Red Blue Green Stripe Flash

US$280

10ct 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)

Add to Wishlist

Purple Striped Boulder Opal 28.1 ct

US$275

Natural Solid Untreated Australian Boulder Opal Polished Stone
Weight: 28.1 carat
Dimensions: 27×19×5.5 mm
Source: Winton, QLD, Australia

Add to Wishlist

39.17ct Double Sided Koroit Boulder Opal

US$270

100% Natural Polished Boulder Opal
Weight: 39.17 ct
Dimensions: 32x23x7 mm
Source: Koroit,QLD, Australia

Add to Wishlist

78.76ct Large Boulder Opal Teardrop Veins

US$270

100% Natural Polished Boulder Opal
Weight: 78.76 ct
Dimensions: 45.5×22.5×8 mm
Source: Koroit,QLD, Australia

Add to Wishlist

7.52ct Natural Boulder Opal Blue Fire

US$255

100% 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

Add to Wishlist

18.44ct Natural Boulder Opal Deep Purple Fire

US$250

100% Natural Boulder Opal
Weight: 18.44 ct
Dimensions: 28x15x5 mm
Source: Winton, QLD, Australia

Add to Wishlist

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

Add to Wishlist

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

Add to Wishlist

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

Add to Wishlist

2.18 ct Natural Boulder Opal

US$240

Weight: 2.18 ct
Dimensions: 13 x 6 x 2.7 mm
Origin: Winton, Queensland, Australia
Size and weight are approximate

Add to Wishlist

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

Add to Wishlist

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

Add to Wishlist

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

Add to Wishlist

34.75ct Large Natural Koroit Boulder Opal

US$227

100% Natural Polished Boulder Opal
Weight: 34.75 ct
Dimensions: 38×22.5×7 mm
Source: Koroit,QLD, Australia

Add to Wishlist

14.43ct Boulder Opal Purple Blue

US$220

100% Natural Boulder Opal
Weight: 14.43 ct
Dimensions: 31×11.5×4.5 mm
Source: Winton, QLD, Australia

Add to Wishlist

1.57ct Natural Boulder Opal

US$215

100% Natural Solid Boulder Opal Polished Stone
Weight: 1.57 ct
Dimensions: 12x6x2 mm
Source: Winton,QLD, Australia
Size and weight are approximate

Add to Wishlist

3.03ct Natural Boulder Opal

US$215

100% 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

Add to Wishlist

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

Add to Wishlist

4.31ct Natural Boulder Opal Vivid Blue Green

US$165

4.31ct 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)

Add to Wishlist

32ct Natural Boulder Matrix Opal Koroit Australia

US$165

Opal 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.