How to Identify Cabochons & Rough Gemstones

Gemstones are characterized as precious, such as diamond, ruby, emerald and sapphire; and semi-precious, such as lapis lazuli, bloodstone, amethyst and garnet. The term "cabochon" refers to thea dome-shaped type of cut used to shape the gemstone. In “Firefly: Guide to Gems,” Cally Oldershaw writes, “Gems that are heavily included or flawed, colored or patterned, opaque or translucent are generally… cut as a cabochon.” Jewelers will polish the gemstone as well as implement this cut to save these questionable gemstones and design different jewelry settings to accent their beauty.

Look at the shape of the gemstone. An uncut, unshaped stone is characterized as a raw or rough gemstone. These uncut stones are sold as geodes, which are hollowed stones lined with multiple crystals pointing inward.

Examine the inside rough structure of the raw semi-precious gemstone geode. It is composed of three parts: quartz, agate and chalcedony.

Look at the center of the geode. The center crystal formation of the gemstone is referred to as quartz and generally has the natural, deep, rich color of the gemstone.

Examine the second or middle layer, which is referred to as the agate. It is characterized by curved bands, also referred to as zones, which have differing colors.

Look at the third or outer layer, referred to as chalcedony. Chalcedony is characterized by a uniform color, and is often used when cut as an ornamental stone. This popular stone is also used for carving as well as sculpture and is characterized as a tough stone. It is available in large, unbroken lumps.

Look at the stone’s shape. A stone with a dome-shaped and polished top is a characteristic of a cabochon.

Feel the dome shape for any cuts. An unfaceted dome shape is another characteristic of the cabochon.

Turn the dome-shaped stone over. A flat and unpolished back side is another cabochon feature.

Hold the ruby close to your eye as if you were putting in a contact lens. Make sure you have a bright light at a distance. Look through the precious ruby gemstone toward the bright light or lamp.

Tilt the gem as you are looking through it. In a ruby, you will see a rainbow-like reflection with a ghost-like shadow or a double image around it.

Look through the semi-precious garnet gemstone toward the light source and tilt as in step 2. The rainbow-like reflection will not have a double image or shadow as the ruby gemstone.