Diamonds are prized and valued around the world, and because of that there are many fakes on the market. Even when one is found in a diamond-rich area, it may be difficult to tell a diamond from other gemstones and minerals. Diamonds are found in many colours, shapes and sizes, as are other precious stones. A few simple tests will help you determine whether your uncut stone is really a diamond.
Shine a bright flashlight through your stone. If it is a real diamond, the light coming through the other side will be white.
Scrape the diamond across a piece of scrap flat glass. If the stone is a diamond, it will scratch the glass.
Turn off all lights in the room. Turn on the black light. The diamond will glow blue if it is real. If it glows another colour, it is probably a different mineral or semi-precious stone.
Breathe on the stone. If it is a diamond, it will not fog up.
To be completely certain that your diamond is real, take it to a jeweller or lapidary shop to get an expert opinion. Cubic Zirconia (synthetic diamonds) can be almost as hard as real diamonds and can scratch glass.
Do not attempt the glass-scratching technique on glass which you do not wish to damage. A real diamond will leave a permanent scratch on glass and other materials. Use caution when purchasing uncut diamonds, as they may not be genuine. Be sure the source is reliable and trustworthy.