amorphous, which means it lacks a repeating crystalline structure. Instead, it is composed of randomly arranged silica spheres or silica chains embedded in water. This random arrangement gives opal its unique and colorful appearance.
Opal is primarily made up of hydrated silicon dioxide (SiO2 ยท nH2O), with a water content ranging from 3% to 21%. The water molecules are loosely bonded to the silica, and this hydration is responsible for opal's play-of-color phenomenon.
Opal can also contain impurities and trace elements, which contribute to its coloration. These impurities can include iron, manganese, and organic compounds.
Furthermore, opal can have various internal structures that affect its optical properties and play-of-color. These internal structures are classified into three main types:
1. Precious opal: This type of opal displays a prominent play-of-color caused by the interference and diffraction of light passing through the silica spheres or chains. The arrangement of these spheres or chains is responsible for the unique patterns and colors observed in precious opal.
2. Common opal: Unlike precious opal, common opal lacks a play-of-color. It has a more uniform and evenly distributed arrangement of silica spheres or chains.
3. Fire opal: This type of opal is known for its vibrant orange, red, or yellow coloration. Although it may display a play-of-color, it is primarily valued for its intense base colors caused by the presence of iron oxide or hematite in the structure.
The internal structure of opal can be observed under a microscope or using advanced techniques such as X-ray diffraction or electron microscopy. These methods help in understanding the arrangement of silica and water molecules within the opal structure and its impact on its optical properties.
The internal structure of a common opal is
1 answer