Ruby Sapphire Facet / Faceting Information


Songes RubyRuby (Sapphire)

Color: Red, red with purple or orange highlights
Moh’s Hardness: 8.5-9
Refractive Index: 1.766-1.774
Critical Angle: 34.62°
Specific Gravity: 3.99-4.01
Cleavage: None
Fracture: Conchoidal
Dispersion: .013
Heat Sensitivity: Can be… but is usually not a problem
Dichroism: strong, especially in darker colors
Birefringence (double refraction): Weak (.018)
Crystal structure: Hexagonal, trigonal, dipyramidal

Treatments: Assume about any Sapphire you see has been heated unless otherwise noted from the supplier. Heat treating to reduce silk is and improve colors is standard. Glass-filling voids in rubies (any sapphire) is not considered an acceptable treatment, by me at least.

What I prefer to polishing with: Zinc laps with 8,000 pre-polish and 50,000 polish.

Jeff’s Comments: Orientation for the best color can take experience and is often not easy for a beginner. Be sure and examine your rough in all lighting conditions when deciding orientation for cutting. Be careful… Sapphire cuts and polishes faster on some sides of the crystal because the hardness varies depending on the direction. It typically will have some pits on some facets (depending on the crystal direction) that need to be polished out. Orientating on the “c” is usually better color. Quality rough is difficult to come by…

Synthetic is usually called corundum and is available in many colors.

Design Links: 4-Way Stop – This is great for saturated rough if you have a piece that will work in the shape…
Princess – Nice in about any material
Brilliant Pear – Good in any color

Gram Faceting Archive of Information
This edited version of an article by the late Jeff Graham is part of a special archived informational series from Gram Faceting. Used with permission.