I HAVE BEEN SELLING ON EBAY SINCE 1999. THER SEEMS TO BE A LOT OF CONFUSION WHEN IT COMES TO PURCHASING A LOOSE GEM, EITHER PRECIOUS, DIAMOND, RUBY,EMERALD OR SAPPHIRE OR SEMI PRECIOUS OR EXOTIC. THIS GUIDE WILL HELP THE CUSTOMER MAKE A CORRECT DECISION ON GEMSTONES! LOOSE GEMS HAVE NOT YET BEEN MOUNTED IN JEWELRY, OR MAY BE FOR A GEMSTONE COLLECTOR. THERE ARE MANY RULES TO CONSIDER BEFORE PURCHASING THEM. THE 4 C'S, CLARITY, CARAT WEIGHT, COLOR AND CUT ARE IMPORTANT, BUT IN SOME GEMS ONE C CAN BE MORE INPORTANT!!!!!!! COLOR!!!!! IN COLOR COLOR CHANGE GEMS  THE % OF COLOR CHANGE IS THE MOST INPORTANT[ALEXANDRITE,GARNET,SPINEL SAPPHIRE AND MORE. COLOR CHANGE CAN BE MILD, MODERATE, OR STRONG!!!!!!!! ASK THE SELLER ABOUT THE COLOR CHANGE IF YOU CAN BEFORE YOU BUY!!!!!!!! A LOOSE GEMSTONE MAY BE MOUNTED IN A RING, PENDANT, BRACELET, EARRINGS ETC. SIZE AND CARAT WEIGHT OF THE GEM- SOME GEMS CAN BE FOUND IN LARGE CARAT WEIGHTS AND SIZES AND SOME CANNOT!!!!!! PERFECT DIAMONDS ARE KNOWN TO EXSIST UP TO 700 CARATS! NATURAL COLORED DIAMONDS[ NOT IRRADIATED] AND [CERTAINLY NOT LAB CREATED OR MAN MADE, WHICH HAVE A VERY LOW VALUE!!!!!!] ARE VERY EXSPENSIVE AND NEVER GET TO THE CARAT WEIGHT OF THE DEBEERS 700 CARAT FLAWLESS COLORLESS DIAMOND. RARE GEMS- WHAT RE THE RAREST GEMS????? BIXBITE[RED BERYL] AND AMMOLITE. BOTH ONE SOURCE GEMS[BIXBITE IN UTAH IN THE USA AND AMMOLITE IN ALBERTA, CANADA] SINCE THESE ARE  SO RARE, CHANCES ARE YOU HAVE NEVER HEARD OF THEM!!!!!!!! GEMS ARE MILLIONS OF YEARS OLD!!!!!!!!! THEY CAN BE WORTH[THE HOPE DIAMND] 220 MILLION DOLLARS APPRAISED NAD IN THE SMITHSONIAN MUSEUM IN WASHINGTON, DC USA AND OWNED BY THE PEOPLE OF THE UNITED SATES OF AMERICA. THIS BLUE DIAMOND WEIGHS ABOUT 44.5 CARATS AND IS NOT FLAWLESS!!!!!!!!!!! IT IS THE MOST FAMOUS GEM OF ANY KIND IN THE WORLD. EXOTICS INCLUDE TANZANITE, TSAVORITE, ALEZANDRITE ,IMPERIAL TOPAZ, ANDESINE, AND MANY MORE INCLUDING DIAMONDS IN RARE COLORS. AS A GENERAL RULE, ALWAYS BUY THE HIGHEST QUALITY YOU CAN AFFORD,  THESE GEMS AND JEWELRY ALWAYS GO UP OVER TIME AND ARE GREAT INVESTMENTS. AVERAGE QUALITY GEMS AND JEWELRY DO NOT GO UP, BUT STILL MAKE SENSIBLE BUYS BUT NOT FOR INVESTMENT PURPOSES!!!!!!! I RECCOMEND THE BOOK "GEMSTONES OF THE WORLD". BUY ONE, TAKE THE TIME TO READ IT AND YOU WILL LEARN MUCH!!!!!!!