Basic Ways to Identify a Ruby
Unless the ruby was collected directly from the source, or is still uncut, it can be tough to determine if the rock in that ring is actually a ruby or something that looks like one without expensive lab equipment. There are a number of methods to distinguish between rubies and gems that look like them, though many rely on the judgement of the observer.
Identifying Fake Rubies
One of the oldest practices for making lookalike gems is gluing colorless crystals together with colored glue (illustrated by the red line). Based on how the colorless material is faceted, the red color (and any other color) will be reflected through the whole gem. It is also one of the easiest imitation gems to identify as the stone will be colorless through the girdle. For other types of assembled gems, a line between the assembled pieces is always visible, if faint. Gas bubbles are also visible with basic 10x magnification from something like a loupe , often resembling flattened doughnuts no matter how well glued together the pieces are.
Diagram of an Assembled Stone
Note: Natural rubies can have gas bubbles, but they are usually weirdly shaped and not always recognizable as gas bubbles.
Judging Luster
When distinguishing between types of red gems, rubies have a sub-adamantine luster (a very high luster). Ruby’s high hardness of 9 on the Mohs scale means that their high luster is second only to diamonds, the only gem that has an adamantine luster. When compared to a piece of glass with a vitreous luster, rubies and diamonds reflect light much more. Judging luster does take some practice and a bit of reference, but it is a very easy observation that can tell the observer about whether they are looking at a ruby or glass. Before making a final judgement on luster, make sure the gem you are looking at is clean. Otherwise you will be judging the luster of your finger grease instead of the gem.
Judging Weight
Rubies are incredibly dense, and will weigh more for their size than other gemstones. This means they will feel much heavier than something like glass at the same size. Unfortunately this test is limited to gems that have not been set in jewelry yet and is a very imprecise test. Also, the smaller the stone is, the less precise this test is. Even with lab equipment, precisely judging the density and carat weight of extremely small, individual stones can be a problem. However, even small stones will bounce on your hand differently.
Mohs Scale
| Stone | Hardness |
|---|---|
| Diamond | 10 |
| Corundum | 9 |
| Topaz | 8 |
| Quartz | 7 |
| Orthoclase | 6 |
| Apatite | 5 |
| Fluorite | 4 |
| Calcite | 3 |
| Gypsum | 2 |
| Talc | 1 |
Magnification
Basic 10x magnification is one of quickest and easiest ways to check if the red gem in your ring is a ruby or something else. Gas bubbles in assembled stones, border lines between pieces, and natural characteristics all become more visible. To top it all off, most jewelry stores will have loupes available for use, and you can get your own for less than $10. Higher magnifications are available and inexpensive too, though after 30x magnification you use a microscope.
Assembled items aside, rubies have unique inclusions like fingerprints. As the name implies, they look a lot like fingerprints, though the exact appearance can vary. Fingerprints in rubies are very characteristic and unique to corundum, the mineral species of rubies (they are also in sapphires, another variety of corundum).
The caveat to spotting this inclusion is that it can be formed in synthetic rubies too as a characteristic of the corundum mineral, instead of forming in a natural environment. Synthetic rubies are chemically the same as natural rubies, the only difference being that they were man-made in a lab instead of the earth. If nothing else, fingerprints guarantee you are dealing with a type of ruby.
Another characteristic inclusion in rubies is called silk. This silk is actually fine rutile needles arranged in three directions, and can diffuse light in rainbow colors as seen under magnification. This is also a mineral crystal that does not form inside rubies from a lab, which means they guarantee the ruby is natural.
With magnification, or even without it depending on how much stuff is in the ruby, any silk included crystals is a guarantee that the ruby formed naturally. Silk also gives a lot of information about heat-treatments done in rubies since the rainbow colors fade with low-temperature heat treatment. This inclusion is also what makes the star in star rubies. Note: synthetic star rubies can be made, but the star is created with synthetic rutile needles only on the surface.
(Examples of what is found in common synthetic rubies)
The most common synthetic rubies will show curved striae and unusually elongated gas bubbles. These are a guarantee that the ruby is synthetic, and often very easy to spot. Another type of synthetic rubies can show fingerprints, which cannot be used to differentiate synthetic and natural rubies.
Trained gemologists can use fingerprints, silk, and other inclusions to identify a ruby with basic magnification alone. They can even determine if it has been heat-treated or not, though some rubies are easier to evaluate than others. Additionally not every ruby shows these inclusions, though they are very common.