| Moonstone | |
|---|---|
 | |
| General | |
| Category | Tectosilicateminerals,feldspargroup,alkali series,orthoclasevariety |
| Formula | (Na,K)AlSi3O8 |
| Crystal system | Monoclinic |
| Identification | |
| Color | Can be numerous colors, including blue, grey, white, pink, peach, green and brown, as well as colorless |
| Cleavage | perfect |
| Fracture | uneven to conchoidal |
| Mohs scale hardness | 6.0 - 6.5 |
| Luster | Opalescent |
| Streak | white |
| Specific gravity | 2.54–2.66 |
| Optical properties | for orthoclase and sanidine, biaxial (–); for oligoclase, biaxial +/– |
| Refractive index | 1.518–1.547 |
| Birefringence | 0.005–0.01 |
| Dispersion | 0.012 |
Moonstone is asodiumpotassiumaluminiumsilicate ((Na,K)AlSi3O8) of thefeldspar group that displays apearly andopalescentschiller.[1][2] An alternative name for moonstone ishecatolite[2] (from goddessHecate).
The namemoonstone derives from the stone's characteristic visual effect, calledadularescence (or schiller), which produces a milky, bluish interior light. This effect is caused by lightdiffraction through alternating layers of orthoclase and albite within the stone. The diffracted light varies from white to blue, depending on the thinness of the albite layers.[1] More technically, this micro-structure consists of regularexsolution layers (lamellae) of different alkalifeldspars (orthoclase and sodium-rich plagioclase).
Polished moonstones often displaychatoyancy ("cat's eye" effect), where a luminous streak appears through the stone.Asterism is rare and produces four-legged stars.[1]
The most common moonstone is of theorthoclasefeldsparmineraladularia, named for an early mining site near Mt. Adular inSwitzerland, now the town of St. Gotthard.[1][better source needed] A solid solution of theplagioclasefeldsparoligoclase +/− the potassium feldspar orthoclase also produces moonstonespecimens.
Deposits of moonstone occur inArmenia (mainly fromLake Sevan),Australia, theAustrian Alps,Mexico,Madagascar,Myanmar,Norway,Poland,India,Sri Lanka,and theUnited States.[2][3] Historically, the most valuable, transparent moonstones with strong blue sheen came from Myanmar.[1] Today, most commercial moonstones come from Sri Lanka.[3]
Moonstone is a type of feldspar that comes in several varieties. All moonstone varieties show adularescence, which creates a soft, flowing sheen that moves across the stone's surface. This effect results from light interference caused by alternating internal layers of albite and orthoclase feldspar.[4]
Gemologists classify moonstone into several distinct varieties. Blue moonstone represents the finest variety of labradorite moonstone, with high transparency and strong blue adularescence. Blue moonstone can be found in Myanmar (formerly Burma), India, Madagascar, Malawi, Sri Lanka, and Tanzania. Labradorite moonstone belongs to the plagioclase feldspar group and forms within the triclinic crystal system, appearing in colorless, white, slight orange, or green varieties with a blue sheen. Orthoclase moonstone belongs to the monoclinic crystal system and displays a mystical white glow in colorless to white, orange, yellow, or brown hues. Gem enthusiasts often refer to adularescent labradorite with a multi-colored glow as "rainbow moonstone," which is colorless and highly transparent. Adularia, named after the Adular Mountains of Switzerland, forms in hydrothermal veins in mountainous regions as colorless to white, cream, pale yellow to pink, or reddish-brown, glassy, prismatic, twinned crystals that frequently display a white to blue sheen.[4]
Moonstone has been used injewellery for millennia, including ancient civilizations. TheRomans admired moonstone, as they believed it was derived from solidified rays of the Moon.[5] Both the Romans andGreeks associated moonstone with their lunar deities. In more recent history, moonstone became popular during theArt Nouveau period; French goldsmithRené Lalique and many others created a large quantity of jewellery using this stone.[6]
The moonstone is theFlorida State Gemstone; it was designated as such in 1970 to commemorate theMoon landings, which took off fromKennedy Space Center. However, it does not naturally occur in the state.[7]
InThailand, moonstone is known asMukdahan, the same name as thenortheastern province next to the riverMekong,Mukdahan. The name of the province comes from a folklore that a magical gemstone looked like a pearl floating above the Mekong in the area where the province is now located.[8]
Media related toMoonstone at Wikimedia Commons