Amethyst cutting files and 3D models

Cutting amethyst (quartz)

Amethyst is purple quartz, and quartz has one of the lowest refractive indices of the common faceting materials. Its critical angle is large, so designs made for diamond window badly unless the pavilion is steepened. It is also a favourite first stone for cutters, and quartz is where most faceting designs are first tested.

Amethyst often shows colour zoning. Cutters orient the rough so the darker zone sits low in the pavilion, where the facets spread its colour across the face-up stone.

Amethyst optical properties

Where a property has a range, angles are calculated from the lower refractive index, which gives the stricter limit.

Every cut, measured in amethyst

For each cut we measured how much of the pavilion, seen face-down, is steeper than amethyst's critical angle of 40.4°, so that head-on light reflects instead of leaking out of the back. Weights are for each model at its reference size.

Amethyst: questions

Other gemstones

• Diamond
• Moissanite
• Cubic Zirconia
• Ruby
• Sapphire
• Emerald