Freeform cabochon of Queensland Australian boulder opal, measuring 10 × 6.5 × 5 mm and 3.4 total carats (opal plus ironstone matrix). Small in size but with its own personality: the multicolored flashes of opal emerge from the earthy ferruginous matrix in a compact format ideal for earrings, small pendants, or minimalist jewelry pieces with geological character. Unique piece numbered no.9.
Piece Details
| Mineral |
Australian Boulder Opal with ironstone matrix |
| Scientific name |
SiO₂·nH₂O in ferruginous sandstone matrix |
| Hardness |
5.5–6 Mohs (opal) / 7 Mohs (quartzitic sandstone) |
| Crystal system |
Amorphous |
| Origin |
Queensland, Australia |
| Dimensions |
10 × 6.5 × 5 mm (freeform) |
| Weight |
3.4 carats (opal + matrix) |
| Play of color |
Multicolored emerging from earthy matrix |
| Matrix |
Ironstone (ferruginous brown sandstone) |
| Finish |
Polished in the opal area |
| Treatment |
Untreated |
| Unique piece |
Yes — numbered piece no.9, one of a kind |
Piece Characteristics
Despite its compact dimensions (10 × 6.5 mm), this piece condenses all the characteristics of Australian boulder opal into a manageable format for small jewelry pieces. The 5 mm thickness is notable for the cabochon's dimensions, indicating that the opal vein has good depth within the matrix.
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Organic freeform: the outline follows the natural shape of the ironstone nodule, without geometric adjustment. Each freeform boulder piece is completely different from any other.
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Compactness: the 10 mm maximum length allows for use in paired earrings, small pendants, or as a secondary accent in larger compositions.
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Opal-matrix contrast: the transition between the iridescent opal zone and the matte, earthy texture of the ironstone is visible from the side profile.
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3.4 carats: total weight including matrix. Proportional to the size of the piece, without excessive weight for earrings.
Jewelry Applications
The small format (10 × 6.5 mm) of this piece is suitable for projects that require smaller scale gems:
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Individual earrings: a single piece in a minimalist 925 silver earring with a closed bezel setting. The asymmetrical freeform adds character.
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Non-identical paired earrings: combined with another boulder piece of similar dimensions, it creates earrings where each piece is distinct but the material unites the set.
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Small-scale pendant: ideal for delicate pendants on a thin chain, where the small scale of the opal contrasts with the delicacy of the metal.
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Secondary element in compositions: can act as an accent in a larger piece that features another mineral as the main focus.
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Compact wire wrapping: small freeforms are popular in minimalist wire wrap with 2-3 coils of 925 silver.
Boulder Opal Care Guide
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Cleaning: soft, slightly damp microfiber cloth. Avoid prolonged immersion in water.
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Avoid ultrasonics: can create microfractures at the opal-ironstone interface.
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Avoid steam: intense humidity can alter the internal structure of the opal.
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Avoid impacts: hardness 5.5–6 Mohs. Store separately from harder gems like quartz or corundum.
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Storage: in an individual padded case.
History and Origin
Queensland boulder opal is primarily mined in the outback region, in deposits such as Yowah, Quilpie, and Koroit. The formation process began 60–100 million years ago when silica-rich water penetrated cracks in sedimentary ironstone nodules. As it slowly evaporated, the silica formed layers of nanospheres with a periodic structure that diffracts visible light, producing the characteristic play of colors. Miners work individually, excavating with hand tools to avoid damaging the fragile nodules.
Frequently Asked Questions
Does the boulder opal in this piece have a visible play of color?
Yes. The multicolored flashes are visible in the opal zone of the piece, which emerges from the earthy ironstone matrix. The play of color changes with the viewing angle and light intensity. Being a compact piece, the active opal area is proportional to its dimensions (approx. 10 × 6.5 mm).
Is it feasible to use this piece for everyday earrings?
With the usual precautions for opal (avoid impacts, sudden temperature changes, and chemical exposure), this piece is suitable for regular use earrings. The 3.4 ct total weight is light for earrings. A closed bezel setting in 925 silver is the safest option for daily wear.
Is the ironstone matrix an integral part of the piece or can it be removed?
In boulder opal, the opal vein and the ironstone matrix are inseparable: they are mineralogically bonded. Attempting to separate the opal from the matrix would destroy the piece. The matrix is a defining characteristic of boulder opal, not a defect.
Note: Crystal meanings are spiritual supports, not substitutes for medical prescriptions.
