Rhinestones are bits of faceted glass.  Glass beads, as well as gems, were used and revered by the ancients.  Many centuries ago in Europe, "paste" (brilliant, clear, hand cut glass, sometimes layered with a thin slice of diamond) was used to create the illusion of "the real thing."     
  
The original "rhinestones" (pebbles of rock crystal) came from the river Rhine.  These Rhine-Stones gave way to mass-produced glass rhinestones.  Most are backed with gold, silver, or tinted foil, or tin, to simulate dazzling gem colors.  Finer rhinestones are hand-faceted and polished, many are hand-set within prongs.  Unfoiled rhinestones usually have a high lead content creating fire and sparkle.  These are referred to as crystals.  Austria and the former Czechoslovakia are noted for crystals.   
 

• * Store pieces of rhinestone jewelry individually as rhinestones scratch.
• * Never (please!) get rhinestones near water, as liquid will tarnish the foil backing and, in older pieces, loosen glued-in rhinestones.
• * Clean with Q-tip dampened in rubbing alcohol.
• * To replace glued-in rhinestones, be sure size, shape and color match exactly before inserting.  Use Epoxy 330, or take to your jeweler.