Gemstones are cut on a faceting machine featuring a spinning disc known as a lap that is infused with polishing compounds such as Diamond powder and other hard minerals like Corrundum. Facets are slowly grind down at precise angles to enhance a gemstones brilliance, dispersion and or color.
A faceted Gemstone is a geometrically shaped gem with flat polished faces. A non faceted Gemstone is a gem that doesn't have a geometrically shaped polished face such as a cabochon.
Gems polished into domes are called cabochons or cabs. These type of gems date back to ancient times and have remained popular in the centuries since. Lapidaries cab certain gem species, such as Opals & Moonstone, to better display visual effects such as play of color, cat's eye, & asterism. In faceted Gemstones these effects would be less visible. Some stones may be cut into cabochons because they're lower quality or too opaque for faceting. Cabbing these stones would emphasize their color and luster rather than brilliance. Softer gem materials may also receive cabochon cuts, since cabs don't show scratches as easily as faceted gems do. Cabochons typically are circular or oval shapes.
They can be found in square or rectangular shapes. In those cases they will show soft curves. Although, they can be found in these shapes they technically aren't considered a standard cabochon, but rather a loaf cut or sugar loaf cut.