How are the colors of natural stones formed?

The colors of natural stones are determined by the minerals, chemical compositions, crystal structures and formation processes of the stones. Each natural stone can have unique color tones due to the combination of different elements and minerals. Here are the basic factors that explain how the colors of natural stones are formed:

1. Chemical Composition

The colors of natural stones are formed depending on the chemical elements they contain. When some elements are included in the structure of the stone, certain colors emerge.

• Chromium: Gives the green color to stones such as emerald and jade.
• Iron: Creates purple in amethyst, green or yellow in tourmaline, and gives reddish tones to hematite.
• Titanium: Gives blue color to sapphire.
• Copper: Gives blue and green tones to turquoise and malachite stones.
• Manganese: Creates pink and red colors in stones such as rhodochrosite.

2. Inclusions (Additives)

Foreign substances or inclusions found in the internal structure of stones can also have an effect on color formation. These substances can cause light to scatter and reflect differently within the stone, creating different color effects.

• Rutile Needles: Forms gold or red colored streaks in stones such as rutile quartz.
• Chlorite and Pyrolusite: Can create green and black tones in stones such as quartz.

3. Crystal Structure and Light Interaction

The crystal structure of stones affects how light is refracted, reflected and absorbed within the stone. These interactions determine the stone's color tones and play of light.

• Pleochroism: The appearance of different colors when the stone is viewed from different angles. For example, this feature is observed in tanzanite and iolite stones.
• Iridescence: Color plays resulting from the reflection of light by thin mineral layers. This feature is seen in stones such as opal and labradorite.

4. Isotopes and Elemental Changes

In some stones, the displacement of isotopes or elements can cause color changes. For example, in the mineral corundum, aluminum can be replaced by iron, titanium or chromium, changing the color of the stone.

• Chromium: Gives ruby ​​its red color, while titanium and iron in the same mineral structure make sapphire blue.
• Manganese: Creates the orange-red hues of spessartine garnet.

5. Irradiation and Heat Treatment

Some natural stones may undergo color changes through natural processes or human intervention, such as irradiation or heat treatment.

• Blue Topaz: Usually colorless topaz turns blue with irradiation followed by heat treatment.
• Amethyst: It turns purple through natural irradiation.

6. Flaws and Gaps

Defects, voids or the presence of foreign elements in the crystal structure of the stones can cause color changes.

• Zircon: It can often be brown or yellowish in color due to defects in its crystal structure.

Conclusion

The colors of natural stones are formed depending on their mineralogical structure, chemical composition, crystal structure and additives such as inclusions in the stone. Each stone gains a unique color and appearance with the combination of these factors. The environmental conditions in which the stone is formed and the changes it undergoes over time can also affect its color tones and brightness. These factors are among the main elements that make natural stones unique and valuable.