Moonstone is translucent bluish-silver feldspar. Its name was given to the stone for blue or silvery-white overflows, which are generated by a thin-plate structure. Moon stones can be milky white, lilac or as if illuminated by inner golden shimmer.
There are lunar stones with stellate patterns or the effect of "cat's eye," but such gems are very rare.
Moonstone is a kind of potassium feldspar orthoclase, which has nothing to do with the Moon. The composition of the stone KALSi3O8, is alumotriosilicate potassium. It crystallizes in the monoclinic system. The effect of the moonstone can be found in plagioclases (oligoclase-white-morolite and albite), as well as orthoclase (not adularia). The color is usually white, light gray or bluish. Processing in the form of a cabochon reveals flickering color changes in blue tones, reminiscent of moonlight, which gives the stone a special attraction. The crystals are translucent. Glitter is silky, glass. The specific optical effect observed in moonstone, as well as in other types of iridescent feldspars, is called shillerization. It weakly luminesces in X-rays. The mineral forms transparent prismatic or lamellar crystals with a bluish-white, "moon" flicker of the surface. Therefore, the moonstone is sometimes called the "fish's eye". There are also crystals of light yellow color. This mineral is extremely rare. Crystals with high quality come mainly from Sri Lanka.
The hardness of it is 6.0-6.6; the density is 2.6 g / cm3. Low refractive indices: from 1.518-1.528 to 1.533-1.535.
This beautiful jewel has its weakness: it is its relatively small hardness. Moonstones should be very carefully processed. Moonstone’s shine can easily be restored by re-grinding and polishing.
Types of moonstones.
Moonstone has several varieties. Sometimes moonstones are called opaque feldspars. One of them - a labradorite - was opened in the XVIII century by missionaries of the German community of the Labrador Peninsula in Canada. A little later, a large Labradorite deposit was found in Russia - in the vicinity of St. Petersburg in 1781, while building a road from St. Petersburg to the Tsar's palace in Peterhof, boulders with labradorite were found.
Petersburg nobility began to wear rings and rings with these gems. By the way, in Russian Empire the moonstone was called tausin - from the Persian word "tausi" - peacock - for resemblance to the overflow of peacock feathers. Labradorite is distinguished by a beautiful game of colors, and its dark variety, sparkling with blue, is called a black moonstone.
The richest deposits of Labradorite were later discovered in Ukraine. And it turned out to be so much that it depreciated, passed into the category of facing stones and was then used for facing underground stations and many monumental buildings. Very beautiful labradorite are mined in Finland and Madagascar (Madagascar moonstone).
Among the feldspars there is also a solar stone (aventurine feldspar), which has an unusual sparkling-golden tint. It is found in Norway, the USA, Russia (on the Selenga River, which flows into Lake Baikal). Another of the varieties of moonstone is albite: translucent, white, with a bluish tint.
But the real moonstones - adularia and sanidine - are still very rare. Their deposits are found mainly in India, Sri Lanka and Burma. And not long ago, geologists discovered large deposits of sanidine in Mongolia.