What gemological tests are used to verify natural stones?

Natural stones are authenticated by various tests in gemology laboratories. These tests help determine the chemical composition, optical properties, physical structure and sometimes the origin of the stone. Here are the main gemology tests used to authenticate natural stones:

1. Refractometer Test

• Purpose: To measure the refractive index of stone.
• How It Works: A refractometer sends light to the surface of a stone and measures the angle at which that light refracts within the stone. The refractive index is used to determine the type of stone.
• Area of ​​Use: It is widely used in the verification of stones such as diamond, sapphire, emerald.

2. Spectroscopy

• Purpose: To examine the light absorption and scattering properties of stone.
• How It Works: Spectroscopy measures the wavelengths of light passing through the stone, and this data provides information about the chemical composition of the stone.
• Area of ​​Use: It is used especially to determine whether the stone is natural or synthetic. It is common in precious stones such as ruby, sapphire, emerald.

3. Microscopic Examination

• Purpose: To study the internal structure of the stone, its inclusions (internal defects) and surface features.
• How It Works: Under high magnification, inclusions, cracks, or healing treatments (e.g., oiling, filling) within the stone are examined.
• Area of ​​Use: The presence of natural inclusions in stones such as emerald and ruby ​​is used to understand whether the stone is natural or not.

4. Density and Hydrostatic Weighing

• Purpose: To measure the density (specific gravity) of the stone.
• How it works: The stone is weighed first in air and then in water. The results of these two weighings are used to calculate the density of the stone.
• Area of ​​Use: It is an important test to determine the type of stones such as diamond, sapphire and quartz.

5. Pleochroism (Dichroism) Test

• Purpose: To examine the ability of a stone to appear in different colors from different angles (pleochroism).
• How It Works: The stone is examined under a polaroscope and the color change of the stone is observed from different angles.
• Area of ​​Use: It is used to verify pleochroic stones such as tourmaline, iolite, tanzanite.

6. Fluorescence Test

• Purpose: To examine the colored fluorescence that the stone shows under ultraviolet (UV) light.
• How It Works: The stone is examined under short or long wavelength UV light and its response (color change, luminescence) is recorded.
• Area of ​​Use: It is used to determine the fluorescence properties of stones such as diamond, sapphire and opal.

7. Absorption Spectroscopy

• Purpose: Identification of the elements responsible for color formation within the stone.
• How It Works: The stone is illuminated with white light and which wavelengths are absorbed (absorption spectrum) are recorded.
• Area of ​​Use: Used to analyze the chemical composition of colored stones (e.g. sapphire, emerald).

8. Internal Heat Test

• Purpose: To measure the internal heat resistance of the stone and to determine whether some stones change color with heat.
• How It Works: The stone is heated to a certain temperature and its reactions to heat are observed (e.g., color change, cracking).
• Area of ​​Use: Also known as the thermal shock test, it is used to determine whether some stones are fake or not.

9. Raman Spectroscopy

• Purpose: To identify the chemical structure of the stone.
• How it works: A laser beam is sent to a rock and the way the rock's atoms scatter the light is measured. Raman spectroscopy determines the rock's chemical composition.
• Application: Widely used in the verification of diamond, graphite, quartz and many other stones.

10. X-Ray Fluorescence (XRF)

• Purpose: To identify the elements within the stone.
• How it works: X-rays are sent into the stone and the absorption and re-emission of these rays by the stone is studied. The emission spectrum determines the chemical composition of the stone.
• Area of ​​Use: It is used in the chemical analysis of precious stones such as diamond, sapphire and emerald.

11. Fourier Transform Infrared Spectroscopy (FTIR)

• Purpose: Identification of organic and inorganic compounds.
• How it works: Infrared light is beamed onto the stone and the stone's absorption spectrum is measured. The FTIR spectrum is used to identify the stone's components.
• Area of ​​Use: It is used to determine whether there is filling material in stones such as emerald.

12. Thermoluminescence Test

• Purpose: To determine if the stone has been in contact with any heat or light in the past.
• How It Works: Heat or light is applied to the stone and the amount of light the stone emits is measured. This can help determine the age of the stone or whether it has been heated in the past.
• Area of ​​Use: It is used to determine whether diamonds and some other stones have been subjected to heat treatment in the past.

Conclusion

Authentication of natural stones is carried out through various gemological tests. These tests analyze the optical and physical properties, chemical composition and internal structure of the stone to determine whether the stone is natural and what type it is. Tests such as refractometry, spectroscopy, microscopic examination, Raman spectroscopy and FTIR are among the most commonly used methods for authenticating stones. These tests are critical to determining the value and authenticity of the stone.