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Seed Bead Types

Seed beads can be categorized into four different types: Rocaille - (pronounced "roh-kai") describes any round seed bead with either a round or a square hole. Often irregular in length or shape. ...
Semi-Precious PDF  | Print |  E-mail

Traditionally, common gemstones were classified into precious stones (cardinal gems) and semi-precious stones. The former category was largely determined by a history of ecclesiastical, devotional or ceremonial use and rarity. Only five types of gemstones were considered precious: diamond, ruby, sapphire, emerald, and amethyst. In current usage by gemologists, all gems are considered precious, although four of the five original "cardinal gems" (excluding the now-common amethyst) are usually—but not always—the most valuable.
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There are over 130 species of minerals that have been cut into gems with 50 species in common use.