These optical effects are called phenomena in gemology, and examples of phenomenal gemstones are opal, labradorite and alexandrite. Today however, we'll be taking a look at two very famous varieties of in particular; the moonstone which displays a phenomena known as adularescence and the sunstone which displays a phenomena called aventurescence.
(Top two photos taken on premises at Gemcamp Laboratories, Quezon City, Metro manila, Phils.)
Both of these gem names typically refer to gemstones that belong in the feldspar group, specifically within the orthoclase feldspar type. Moonstone is usually semi-translucent to semi-transparent and can appear in a narrow range of cool colors, the most preferred being a deep, shining blue. This is not to be confused with a similarity to other blue gemstones though. Even the best moonstones are typically white or clear in bodycolor, showing good transparency. The blue we are referring to, is seen as a billowing diffused "fog" of color that rolls within the gemstone upon motion. This almost ghostly appearance is what gives moonstone its popularity.
The effect is actually caused by the interaction of light with the intertwined microstructures of albite and orthoclase within the interior of the moonstone. In a scenario of total darkness, the blue sheen would not appear to the eye. Such phenomenal effects were once considered to possess mystical or healing properties because of their almost celestial appearance.
Next up, we have the glittering shimmer of sunstone. Now this variety of gem-quality feldspar is typically orange, or brownish red. Most of its color however actually comes from a large amount of tiny platelets and inclusions enclosed within its body.
There are actually many gemstones that are labeled with the trade name 'sunstone' today, but we'll be looking at the most famous of them all- the Oregon sunstone. This specific variety of gem, showcases a distinct appearance through a dazzling display of miniature sparkles that glisten through multitudes of reflective copper flakes. This shimmering effect smoothly glides as you tilt or roll the stone, keeping your eyes on the phenomenal visual effect that the trade has come to call aventurescence.
Sunstone's widespread popularity makes it an ideal choice for designer cut gems and sculptures. It's also the target of mass imitation. Several manufacturers produce a similar item called 'goldstone glass' which can resemble sunstone to a certain degree.
Another variety of sunstone has also been gaining popularity due to its unique appearance. 'Rainbow Lattice Sunstone', also belongs to the feldspar group and typically shows iridescent shimmering within its transparent body. This is usually due to an array of reflective mineral inclusions such as hematite and ilmenite, which produce the beautiful phenomena the stone boasts of. Most of this material is found in Australia, along with another famous phenomenal gemstone- opal, which was previously discussed in an earlier blog post.
Photography Credit / Courtesy of Multicolour Gems
