Identifying raw precious stones like diamonds, rubies, sapphires, and emeralds requires careful examination and testing. Precious stones in their uncut, unpolished state can often look very similar to one another and to less valuable stones. However, with some basic knowledge of gemstone properties and access to a few simple tools, you can often determine if a raw stone is a diamond, ruby, sapphire or emerald.
Visual Inspection
The first step in identifying a raw precious stone is a close visual inspection. Examine the color, clarity, surface flaws, and inclusions of the stone. Here are some things to look for:
- Diamonds – Colorless or various tints of yellow/brown. High clarity with few inclusions. Adamantine luster.
- Rubies – Deep red to purplish-red. Lower clarity with flaws visible. Vitreous luster.
- Sapphires – Various colors besides red. Lower clarity. Vitreous to adamantine luster.
- Emeralds – Deep green. Many surface fractures and inclusions. Vitreous luster.
While visual inspection can help narrow possibilities, it’s usually not sufficient to conclusively identify raw precious stones. Additional testing is required.
Hardness Testing
One of the most useful tests for identifying gemstones is hardness testing. This involves rubbing the stone against a set of reference materials with known hardness values. Here is the process:
- Obtain a gemstone hardness testing kit. These include materials like glass, steel, and corundum.
- Rub the stone firmly against each testing material, starting from softest to hardest.
- Compare the scratch pattern on the stone to the known hardness of each material.
- Determine where the stone falls on the Mohs hardness scale.
The Mohs scale ranges from 1 (talc) to 10 (diamond). Here are the hardness values for precious stones:
| Gemstone | Hardness Value |
|---|---|
| Diamond | 10 |
| Ruby | 9 |
| Sapphire | 9 |
| Emerald | 7.5 to 8 |
Hardness testing can help distinguish diamonds and rubies/sapphires from softer stones like emeralds. But it can’t differentiate between rubies and sapphires, which have the same hardness.
Refractive Index
Measuring a stone’s refractive index can further help identify it. This involves using a refractometer to determine how much light is bent when passing through the stone. Here are typical refractive indices:
| Gemstone | Refractive Index |
|---|---|
| Diamond | 2.417 |
| Ruby | 1.762 – 1.778 |
| Sapphire | 1.760 – 1.768 |
| Emerald | 1.570 – 1.585 |
A stone’s precise refractive index can confirm its identity. Overlapping ranges like ruby and sapphire may still require further testing to differentiate.
Chemical Testing
For definitive identification, laboratory gemological testing is needed. This includes:
- Spectroscope – Measures optical spectra produced when exposed to controlled light sources. Can identify unique chemical signatures of different gemstones.
- X-ray fluorescence – X-rays excite a stone’s atoms to emit energy waves. Analyzing these elemental signatures identifies the chemical composition.
- X-ray diffraction – X-ray diffraction patterns reveal a stone’s unique crystal structure. Especially useful for differentiating diamonds, rubies, and sapphires.
Advanced testing like this is the most reliable way to conclusively identify a raw precious stone. But it requires specialized laboratory equipment and expertise.
Summary of Identification Methods
Here is a summary of techniques for identifying raw precious stones:
| Method | Usefulness | Limitations |
|---|---|---|
| Visual inspection | Narrows possibilities | Insufficient for conclusive ID |
| Hardness testing | Helps distinguish diamonds, rubies/sapphires, emeralds | Can’t differentiate rubies and sapphires |
| Refractive index | Confirms a stone’s identity | Overlapping ranges for some stones |
| Laboratory testing | Provides definitive identification | Requires specialized equipment and expertise |
Using a combination of these techniques allows for progressively more certain identification. Visual inspection and hardness testing provide a good starting point. Refractive index measurement adds more precision. And lab testing delivers 100% conclusive results.
Conclusion
Identifying raw precious gemstones takes patience and practice. But with careful inspection, hardness and refractive index testing, and access to professional lab analysis, you can confidently determine if an uncut stone is a diamond, ruby, sapphire or emerald.
Start by examining color, clarity, inclusions and luster. Use hardness testing kits to scratches stones against materials of known hardness. Compare refractive indices measured with a refractometer to known gemstone values. And rely on advanced spectroscopic, diffraction and fluorescence techniques for definitive identification.
Understanding these methods for distinguishing raw diamonds, rubies, sapphires and emeralds allows jewelers, gemologists and collectors to evaluate precious gemstone specimens accurately. With the right knowledge and tools, uncovering the true identity of a raw stone is an achievable goal.
