Diamond vs. Cubic Zirconia: Separating Fact from Fiction

Question
Mr. Lumetta:

I have a question(s) for you.  First, will CZ float in water?  I've heard some people say it does, and others oppose.  Second, can real diamonds that go uncleaned for a while develop a "filmy" residue on the outside of the stone?  Third, is it possible for a CZ to pass the fog test?  This stone I have passed the following tests: The Fog Test, The Light Test [when the stone is put table down on a white piece of water and a penlight is shown up through the bottom there is a halo of light but the center remains darker], Scratches Glass Test [which I believe CZ can also do though], and when held up to light it does sparkle more gray shades.  Are there any other "home" tests that can be done to figure out the stone's composition?  Thank you for your time and consideration.

Jeff

Answer
HI JEFF,

CZ DOES NOT FLOAT IN WATER. DIAMOND HAS A AFFINITY FOR OIL OR GREASE AND WILL GET A DULL LOOK TO IT IF NOT CLEANED REGULARLY. ALL THE OTHER TESTS YOU MENTION THE FOG TEST, THE LIGHT TEST, SCRATCH GLASS TEST ETC. CAN BE DONE WITH A CZ AS WELL AS OTHER MINERALS. JUST ABOUT ANYTHING WILL SCRATCH GLASS INCLUDING CZ. NONE OF THESE TESTS PROVE A STONE IS DIAMOND OR NOT. THE MOST POSITIVE TEST FOR DIAMOND IS THE MOST DESTRUCTIVE, HARDNESS. ONLY A DIAMOND WILL SCRATCH A DIAMOND WITH A HARDNESS OF 10. ANOTHER IS READTHROUGH, PLACE A LOOSE DIAMOND FACE DOWN OVER A TYPED WORD AND YOU SHOULD NOT BE ABLE TO READ THE WORD THROUGH THE BACK OF THE DIAMOND. THERE ARE OVER 20 CHARACTERISTICS OF DIAMOND THAT CAN BE SEEN WITH THE NAKED EYE AND ARE ONLY FOUND IN DIAMOND. YOU WOULD NEED TO TAKE A DIAMOND COURSE IDENTIFYING A WHOLE LOT OF DIAMONDS TO LEARN THEM ALL AND BE ABLE TO USE THEM IN IDENTIFYING A DIAMOND. GO TO G.I.A.'S WEBSITE, www.gia.org FOR MORE INFO AND SOME MORE TIPS. GOOD LUCK

PETER