Gemstones are rare rocks, which are usually processed and incorporated into jewelry and decorative objects. Gemstones have the following characteristics: Beauty. This includes visual aspects such as color, shine, fire, transparency and light effects. Durability. This looks at hardness, fragility/cleavage and chemical resistance. Rarity. This looks at how often a product occurs in nature. Gemstones can be cut in many different shapes. The basic distinction is between cabochon, where the gemstone is cut into a convex shape, and faceted, where the surface of the gemstone is cut into different facets. When cutting, one looks at different properties of the stone, including the color, color distribution, inclusions, special light effects, dispersion and fracture and cutting surfaces. In this way, they are processed into necklaces, earrings, bracelets and many other pieces of jewelry, but the gemstones are also used in industry for processing. Well-known gemstones include diamond, ruby, emerald, sapphire, aquamarine, topaz, tourmaline, amethyst, citrine, carnelian, opal, onyx, turquoise, lapis lazuli and garnet. In the 18th and early 19th century, it was fashionable to make jewelry in which someone's name or initials were incorporated. The choice of gemstones was guided by the first letter of the name of the gemstone, and thus the gemstone alphabet came into being. Similar achrosticon jewelry was also made during the nineteenth century, in which sentiments were expressed in gemstones. The best known is the English 'regard' ring, an engagement ring in which the word 'regard' was formed by the gemstones ruby, emerald, garnet, amethyst, diamond