Opal Faceting Information
Covers essential opal faceting information and related issues, research, tips, and guides about Opal Faceting. Choose what best fits the criteria for Opal.
Opal Faceting Information
Color: Colorless, yellow, orange, red
Moh's Hardness: 5-6.5
Refractive Index: 1.44-1.46
Critical Angle: 43.98°
Specific Gravity: 1.9-2.23
Cleavage: None
Fracture: Conchoidal, brittle, splintery
Dispersion: None
Heat Sensitivity: High to moderate
Birefringence (double refraction): None
Crystal Structure: Amorphous
Treatments: Generally none. However it is very common practice for rough dealers to sell them in water. The Opal absorbs water and weighs more this way. The water will also hide flaws and cracks. Never buy Opal in water. Mexican opal should be "seasoned" by leaving it open to the air for at least a few months before cutting to assure stability.
What I prefer to polishing with: Cerium oxide on a Tin lap, or a Spectra Ultralap
Jeff's Comments: Cold dop… Use glue when dopping to prevent damage to the stone by heat. Stones that display opalescent fire are usually better to cut as cabochons.
Design Notes: Use Opal designs and some Quartz designs that have been adjusted for the lower refractive index of Opal.
Jeff R. Graham
The late Jeff Graham was a prolific faceter, creator of many original faceting designs, and the author of several highly-regarded instructional faceting books such as Gram Faceting Designs.
Related Articles
Opal Stones and Gems: Value, Price, and Jewelry Information
Gemstone Doublets, Triplets, and Other Assembled Stones
Tips for Cabbing and Carving Opals
An Interview with Opal Expert Joel Ragan
Latest Articles
A Guide to Early Victorian Romantic Period Jewelry
Malaya or Malaia Garnet Value, Price, and Jewelry Information
Choosing Your First Gemstones: A Rough Guide for Faceters
Gemstone Coatings: CVD and More
Never Stop Learning
When you join the IGS community, you get trusted diamond & gemstone information when you need it.
Get Gemology Insights
Get started with the International Gem Society’s free guide to gemstone identification. Join our weekly newsletter & get a free copy of the Gem ID Checklist!