The very first and possible most important thing people should know before buying diamond's, is the importance of the diamond grading report and certificate. Every diamond should come with a certificate and grading report; preferable from the GIA (Gemological Institute of America) or IGI (International Gemological Report). Any jeweler worth their salt will tell you to never purchase an affordable diamond that does not come with a report. This grading report tells the consumer everything they need to know about the gem, including specific measurements for things like cut, color, clarity, and much more. This is important because, without the certificate and grading report consumers are left guessing as to whether the gem is worth what they paid for, also without this documentation consumers will be hard pressed to find anyone to sell it to if they ever tried. So get that documentation! An outside jeweler's opinion may also help set your mind at ease.
Other things people should know before purchasing loose diamonds include the basic information on what a diamond is and how it is graded. A diamond is made miles underneath the Earth's crust, below the upper mantle, here rocks and material are being melted and reformed into new material. Here the high temperatures and high pressure combine to create the perfect atmosphere for diamond creation. Diamonds form from carbon, which gets trapped in the high heat and pressure, eventually more and more carbon is pressed and heated together until a diamond is formed. Then the Earth does its job and transports this material towards the surface, where it is found.
Diamonds are graded by, among other things, the cut (determines brilliance), color (the less color, the higher the quality), clarity (inclusions or blemishes found), and carat weight (weight measurement of the diamond). These are the characteristics that many a jewelry professional would examine when choosing loose diamonds for a jewelry design, as should you. These are also the characteristics of a diamond that help determine the value and price of the gem. Choosing to purchase a diamond or diamonds is a solid investment, as long as one knows what to look out for.