Moonstones are the highly prized gemstone. The best quality moonstone fetches price more than it is valued. Moonstones are prized for their adularescence – it is an optical phenomenon that creates a cloudy appearance of blue and white light with moonlight sheen. These are the feldspar gems that have varying composition and are found all over the world. They are known as feldspar gems that have different compositions alternating layers of orthoclase and albite. Like the name, the Moon, have inspired a bit romantic lore. Despite it has low hardness and a tendency to chip, moonstone is a very popular choice for jewelry and used in pendants, rings and earrings. Moonstone is cut in the shape of Cabochons and carvings and the transparent stone is faceted.
Usually, the more transparent and colorless body, the more blue adularescence, the higher the value of moonstone. Large quantities of opaque materials with various body colors, are carved into simple “moon faces” and other figures, are available for pennies. Cabochons of translucent material, either, it is present in white or with pleasing body colour and the adularescence, are rarely common in the market and common relatively modest prices.
For cat’s eyes and the occasional star, expect to pay in proportion to the beauty of the eye or star, size, and clarity.
Historically, it is found that most valuable colorless and transparent moonstones with string blue sheen are available in Myanmar. But unfortunately, this material is not found now. Most of the top-grade, blue sheen gems available today are being available from one dealer or collector to another, which escalates the prices.
The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.
A blue soft color is found in orthoclase moonstone if the albite crystals are very fine. The sheen is white if the albite plates are thick. The color of the orthoclase may be white, beige, brown, red brown, greenish, or yellowish. The small amount of red tinge is due to the presence of small amount of goethite inclusions. A moonstone with orthoclase feldspar sanidine is found in Grant County, New Mexico.
There are some transparent plagioclase feldspar, such as labradorite, that have thin layers of albite. These produce a light blue schiller effect if it is found and thin and a white effect if found in thick layer. This phenomenon is known as labradorescence. Such stones are also known as rainbow moonstones or peristerites. Technically, this is a variety of labradorite and not moonstone. Labradorescence is very different from adularescence.
Specific Gravity and Refractive Index
The best specimen of Moonstone is found in Sri Lanka with a specific gravity on the low end of the moonstone scale, 2.56. Specimen from India tends toward the high end of 2.59. The refractive index of most moonstones is usually 1.520-1.525 with a birefringence of 0.005. The material from Virginia has RI of 1.518-1.524 with a birefringence of 0.006.
Myanmar has historically yielded the finest material