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The Mysterious Opal Moisture: How Does Its Moisture Content Affect Quality?
Opal is a hydrated amorphous form of silicon dioxide (SiO2·nH2O), which means its water content can range from 3% to 21%, but usually ranges from 6% to 10%. Opal's physical structure is irregular, so it is classified as a mineral substance rather than a typical crystalline mineral. This special structure makes opal a unique gemstone, with various changes in color and transparency.
Opal's name may be derived from the Sanskrit word "upala", meaning "gem", and the later Greek derivative "opállios" also inherited this meaning.
Opals can be mainly divided into two categories: rare opals and ordinary opals. Among them, Precious Opal is widely loved for its unique color-changing effect, a phenomenon known as "color play." Color play is an optical phenomenon that causes certain minerals to show dazzling color changes under light. This is due to the characteristics of their internal structure that cause light to interfere and diffract.
The quality of precious opal is primarily determined by its internal structure. It consists of silica spheres about 150 to 300 nanometers in diameter, which are arranged in a hexagonal or cubically tightly stacked pattern. This ordered structure can determine the observed color and can present beautiful spectral effects under specific conditions, while the level of water content further affects the absolute refractive index and luminescence ability.
"The quality of opal lies in its moisture content and the degree of orderliness of its microstructure."
The impact of moisture on Opal quality does not end there. Because opal's high moisture content makes it particularly sensitive to environmental changes, it can easily deform or crack due to heat. This property limits opal's use in jewelry making. Therefore, synthetic or compounded opal is often used to achieve similar visual effects, achieving a beautiful appearance at a lower cost than natural opal.
The difference between precious and ordinary Opals
In addition to rare opals, there are also various types of common opals. These include milky-white milk opal, resin opal, and wood-replacement wood opal. These different types typically do not exhibit discoloration but are known for their cloudy white sheen.
"Ordinary Opal shows completely different characteristics from precious Opal through the internal turbid luster."
The history and origin of Opal
Opal was regarded as an extremely precious gemstone in ancient times and was deeply loved by the royal family. Before the 19th century, the only known source was Chalven, Slovakia. It was not until large mineral deposits were discovered in Australia that opal began to enter the market at a lower price. Australia is still the world's main opal producer, and it is estimated that the country's opal production accounts for 95% to 97% of the world's opal production.
Opal from Ethiopia was first discovered in 1994 and subsequently attracted a lot of attention due to its special optical properties. Virgin Valley, located in Nevada, is also an important opal producing area in the United States, producing a variety of precious black and crystal opals.
Conclusion
The influence of moisture on the quality of Opal cannot be underestimated. Through this unique hydration structure, Opal displays countless beautiful colors and diverse gemstone properties. With the further mining of Opal, will new technologies emerge to unlock more secrets of Opal?
