Triangular Australian Opal Cabochon No. 16

Triangular Australian boulder opal cabochon, measuring 18.9 × 11 × 7.25 mm and weighing a total of 15.1 carats (opal plus ironstone matrix).

Piece Details

Piece Characteristics

Boulder opal is a variety of opal in which the opal vein and the ironstone (ferruginous sandstone) matrix are mineralogically inseparable.

• Triangular shape: an unusual geometry for boulder opal. The three angular vertices require specific protection when setting.
• Dark matrix: the ironstone in this piece has a very dark tone that maximizes the contrast with the play of color.
• High chromatic intensity: the play of color covers much of the visible surface of the opal with high-saturation flashes.
• Thickness of 7.25 mm: provides significant presence and optical depth for the piece's dimensions.
• 15.1 carats: total weight including opal and matrix. Proportional to the 18.9 mm triangular size.

Jewelry Applications

The triangular shape (18.9 × 11 mm) and the visual impact of the play of color make this piece the center of designer jewelry projects in 925 silver:

• Closed bezel setting in 925 silver (recommended): the bezel surrounds the three vertices of the triangle, distributing the setting pressure evenly. The organic irregularity of the boulder contour requires manual adjustment of the bezel to the actual contour of the piece.
• Statement pendant: the dimensions and triangular geometry create a central pendant with great visual impact on a 45–60 cm silver chain.
• Artistic occasional ring: with a robust 925 silver mounting to protect the three vertices. The 7.25 mm thickness requires a medium-high profile mounting.
• Wire wrapping in 925 silver: feasible with frameworks that do not exert point pressure on the vertices. Triangular wire wrap compositions are visually very effective.

The dark ironstone matrix pairs especially well with oxidized or blackened silver.

History and Origin of Australian Boulder Opal

Australian boulder opal is primarily extracted from deposits in the outback.

Boulder Opal Care Guide

• Cleaning: soft, slightly damp microfiber cloth. The ironstone matrix is porous; avoid prolonged immersion in water.
• Avoid ultrasonics: vibrations can create micro-fractures at the opal-ironstone interface and within the opal.
• Avoid steam: intense humidity can alter the internal structure of the opal and temporarily darken the matrix.
• Avoid impacts to the vertices: the three angles of the triangle are the most vulnerable points. With a hardness of 5.5–6 Mohs, opal is susceptible to chipping in angular areas.
• Storage: in an individual padded case, separate from other harder gems.

Frequently Asked Questions

What distinguishes this boulder opal from black opal?

Solid black opal has no matrix: it is pure opal with its own dark base.

Does the 15.1 carat weight include only the opal or also the matrix?

In boulder opal, the weight always includes both opal and matrix, as they are inseparable.

Is it feasible to set a triangular shape in silver?

Yes. A closed bezel setting in 925 silver is the most suitable method for angular shapes like this triangle.

Note: The meanings of crystals are spiritual supports and do not replace medical prescriptions.