Gemstone Facets: Terminology and Functions
by Donald Clark, CSM IMG, International Gem Society
Step 1: Introduction to Gemology
Lesson 22
Summary
Facets, those “geometrically arranged, flat surfaces” that cover faceted gemstones, all play specific roles in a gem’s optical performance. When expertly cut, facets not only create beautiful patterns on the gem, they also help it shine. Sometimes, literally. Different types of gemstone facets have specific names, too.
Reading time: 3 min 1 sec
Barion octagon-cut ametrine, 4.48 cts. © Dan Stair Custom Gemstones. Used with permission.
"If you’re new to the art of gem cutting, you’ll become quite familiar with these terms as you learn to facet gems. However, all gem enthusiasts, especially gem buyers, can benefit from learning about the types and functions of different gemstone facets.
The Three Principal Areas of a Faceted Gem
Girdle
The widest part of the gem, the girdle defines its outline. When viewed from the side, however, the girdle is usually fairly thin. Faceters cut girdles to help set the stone in jewelry.
Crown
For both cabochons and faceted gems, the top is called the crown. For faceted gems, this means the area above the girdle. Usually, you’ll see this area when viewing the “face” of a gem set in jewelry.
Pavilion
The bottom of a faceted gem, the area below the girdle, is called the pavilion.
Types of Gemstone Facets
Mains
The largest facets are called mains. (Some gems have larger table facets). There are both pavilion mains and crown mains.
Smoky Quartz, 22 cts, Audrey Lynn Mine, Cahuilla Mtn., Riverside County, California, USA. © Rob Lavinsky, http://www.iRocks.com. Used with permission.
Table Facet
The large, horizontal facet on the top, the table facet acts as a window into the interior of the gem.
Break Facets
Adjoining the girdle, the break facets scatter light, which creates more scintillation or tiny flashes of light. There are both crown and pavilion break facets.
Cushion-cut andalusite, 4.07 cts, Bahia, Brazil. © Rob Lavinsky, http://www.iRocks.com. Used with permission.
Star Facets
The “top row” of facets, star facets adjoin the table facet. Along with the other crown facets, they serve to control the entry and exit of light from the gem.
Rhodochrosite, 3.55 cts, Capillitas Mine, Andalgala, Catamarca, Argentina. © Rob Lavinsky, http://www.iRocks.com. Used with permission.
Pavilion Facets
The pavilion facets are designed to reflect the light back to the viewer. This enhances both brilliance, the amount of light a gem returns, and dispersion, the colorful “fires” that seem to emanate from within.
Culet
The point at the bottom of the pavilion is called a culet. Some gems have tiny, flat culets instead of points. This helps prevent chipping.
Keel... "
https://www.gemsociety.org/article/gemstone-facets/