Faceting Tips For Exotic Gemstones

Exotic gemstones may be minerals that occur rarely in nature or simply gems that are rarely worn as jewelry pieces. Smithsonite is a popular stone for gem collectors. However, despite its high dispersion and rich color, it's too soft to be worn as jewelry. Therefore, it's rarely faceted. “Smithsonite” by Thomas Spann is licensed under CC By 2.0
Exotic gemstones may be rare. Rare in nature or rare in jewelry. Smithsonite is popular with gem collectors.  It has high dispersion and rich color.  However, smithsonite is too soft to be worn as jewelry and rarely faceted. “Smithsonite” by Thomas Spann is licensed under CC By 2.0

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.

Thanks,

Dave G.

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. 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.
Celestite is usually colorless. It's soft, difficult to cut, and has little fire. “Celestine or Celestite” by Free Photos is licensed under CC By 2.0 (Maybe move to 1st pic)
Celestite is usually colorless. It’s soft, difficult to cut, and has little fire. “Celestine or Celestite” by Free Photos is licensed under CC By 2.0
  • 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.
“Dioptase Specimen, Museum Quality” by Cobalt 123 is licensed under CC By-SA 2.0
“Dioptase Specimen, Museum Quality” by Cobalt 123 is licensed under CC By-SA 2.0
  • 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 features a List of Gemstones by Name.  This resource includes all kinds of information on lesser known gemstones and collector items.

Roland B.

The characteristics of some exotic gemstones can vary based on their sources. Most actinolite stones are difficult to facet. However, small specimens from Madagascar are typically clean and well suited for cutting. “Actinolite Schist” by James St. John is licensed under CC By 2.0
“Actinolite Schist” by James St. John is licensed under CC By 2.0