Diamond is perhaps one of the easiest stone to identify. There are many physical properties of diamonds that are unique by itself and these characteristics are not found in other colored stones.
Care must be taken that a synthetic diamond will also pass these tests. Synthetic diamonds have the same properties as natural diamonds except that they are grown in laboratories using various highly technical methods.
The Refractive Index (Read here for RI) is 2.417. This is perhaps one of the highest RI found among gemstones. But RI is never used for identification of diamond as the normal gemological laboratory Refractometer does not read beyond 1.80.
The Specific Gravity (Read here for SG) is 3.52 and because cut diamond is very small in nature (a 5ct or 1gm diamond is considered quite big) SG testing is never used.
As diamond has a very high RI, when you place a Round Brilliant Cut Diamond onto a pencil drawn line or some typed words, there is a no see-through effect, that is, you cannot see the line or the words inside the diamond. In fact this is a quick and dirty test for diamond identification as you can do it everywhere.
Most diamonds have a frosted girdle not found in any colored stones. Cutters normally will leave the girdle frosted in order that this can be identified as a diamond easily. However, some of the girdles are polished, so if you have a polished girdle you cannot jump to conclusion that this is not a diamond.
As diamond is the hardest mineral (Read here for Mohs hardness) hence, it has very sharp facet junctions. If you see a lot of tiny fractures along the faceted junctions of a colorless stone, it is not likely a diamond.
The way a diamond or a colored stone fractures can give a lot of information on the identity of the stone. Diamond is the only stone that has a step-like fracture. (compared this to glass where the fracture is conchoidal, meaning curve-like). If you have a cut diamond and there is a sizeable fracture on it, use a loupe (Read here on how to use a loupe) to view the fracture surface carefully. It is likely that you will see the step-like fracture.
Most diamonds have tiny root-like tendrils protruding perpendicular to the girdle which are called beardings. However, in very well cut diamonds you may not find any of these beardings. If you have beardings then the specimen stone is a diamond.
Trigons are minute triangle-like crystal indentations on a rough diamond. Most cutters will try to retain these trigons on the side of the girdle. But these are rare and the price of a particular diamond with trigons on the girdle have a very high premium.
And of course a diamond tester is the easiest way to identify a diamond. Diamond is a very good conductor of heat. When a diamond tester is switched on, the probe will heat up and when it touches a diamond the heat is conducted away quickly which will be indicated with a small high pitched sound and normally a green indicator will alight. Other stones will not respond to this test. However, Mossainite, a type of synthetic stone, will respond positively to this test and you have to separate it between the two. (This will be dealt with in a future post).
Good luck to you.
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