MyOpal authenticity & grading guide

This guide explains MyOpal product descriptions. It is not an independent certification standard. Read the individual product information for the details of each stone.

Weight, dimensions and origin

Weight is measured in carats; 1 carat equals 0.2 grams. Length, width and depth describe the stone’s size. Measurements may vary slightly. Country of origin is stated where known.

Body tone

Body tone describes the relative darkness or lightness of the opal’s base color, without its play-of-color: N1–N4 black, N5–N6 dark and N7–N9 light. Body tone alone does not determine value. Screen brightness and lighting affect this approximate visual guide.

Dome

MyOpal uses the following descriptive dome categories: high (height-to-width ratio of 0.6 or more), medium (0.3 to below 0.6), low (below 0.3) and flat (no significant curvature). These categories describe the dome's shape; they do not by themselves determine brightness or value.

Opal types

• Black opal: Body tone N1–N4.
• Dark opal: Body tone N5–N6.
• Light or white opal: Body tone N7–N9.
• Crystal opal: Transparent to translucent opal. Black crystal opal combines this transparency with a dark body tone.
• Boulder opal: Opal occurring with its natural ironstone host.
• Opalized fossils: Opal that has replaced or preserved the form of fossil material.
• Fire opal: Transparent to translucent opal with a yellow, orange or red body color, with or without play-of-color.
• Matrix opal: Opal distributed through its host rock. Some Andamooka matrix opal is treated to darken the host material; check the individual description.

Assembled opals

A doublet is an opal layer bonded to a backing. A triplet is an opal layer between a backing and a clear cap. These are assembled or composite stones and should not be described as equivalent to solid natural opal.

Check each product description for details of any treatments, assembly and materials. Contact us if you need clarification.