Question: I’ve received some gemstone rough from my brother. They include some fairly exotic gemstones. Do any fellow gem lovers have any practical information for faceting actinolite, amblygonite, celestite, dioptase, epidote, leucite, and/or smithsonite? Any help on how to approach these exotic gemstones would be appreciated.
By International Gem Society 1 minute read
faceting exotic gemstones - epidote

Rectangular step-cut, bi-color epidote, 10.18 cts, 20.1 x 9.1 mm, Pakistan. © The Gem Trader. Used with permission.

Answer: Check out Faceting for Amateurs by Glenn and Martha Vargas. This book features an appendix that lists most gem materials and includes cutting and polishing information. It also has a section on unusual faceting materials.

Notes on Faceting Selected Exotic Gemstones

Here’s a summary of special notes for your exotic gemstones.

  • Actinolite has very easy cleavage in two directions and requires care. Sharp corners will fray.
  • Amblygonite has perfect cleavage in two directions.
  • Celestite should be kept away from sulfite compounds. It’s extremely heat sensitive and best cut as a round gem.
  • Dioptase is brittle.  Its cleavage may mean trouble on course laps. Use only extra or ultra-fine laps. Use speed of 100 rpm or less for polish.
  • Epidote is easy to cut and polish, but its cleavage may separate during heating. If the rough is a twin, the twinning planes can present problems.
  • Leucite should pose no special problems if cut on fine laps at slow speeds. Keep it wet during polishing.
  • Smithsonite should pose no problems if you avoid the three cleavage planes. Dopping heat with care.

Don’t forget that the International Gem Society (IGS) reference library includes a Gemstone Encyclopedia. This resource includes all kinds of information on lesser known gemstones and collector items.

Roland B.