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Birthstones
Michael Schweska
Physical Geology
Spring 2005
 

                                               June Birthstone-Moonstone

 
In Europe, moonstone is considered the birthstone for June, although in the United States it shares that distinction with Alexandrite and Pearl. Moonstone is 6 - 6.5 on the Mohs scale of hardness. Fine Moonstone is quite rare and becoming rarer. It is mined in Sri Lanka and Southen India. The rainbow variety can also be found in Madagascar. Moonstones are usually cut in a smooth-domed cabochon shape to maximize the effect. Sometimes they are carved to show a man-in-the-moon face. Moonstone beads also display the sheen very well and are simply stunning against a black dress. Moonstone Click here for a picture in natural form. Click here for more faceted and natural specimens.

Description:

Moonstones come in a variety of colors. The body color can range from colorless to gray, brown, yellow, green, or pink. The clarity ranges from transparent to translucent. The best moonstone has a blue sheen, perfect clarity, and a colorless body color. Moonstone almost seems magical with a ghostly shimmering glow floating in a crystalline material. The Romans thought that moonstone was formed out of moonlight. Sometimes moonstone will have an eye as well as a sheen. Another related feldspar variety is known as Rainbow Moonstone. In this variety of labradorite feldspar, the sheen is a variety of rainbow hues.

Chemistry:

The formula for Moonstone, Oligoclase, a variety of Feldspar is Na(90-70%)Ca(10-30%)(Al, Si)AlSi2O8, Sodium calcium aluminum silicate. Oligoclase is not a well known mineral but has been used as semi-precious stone under the names of Sunstone and Moonstone. Sunstone has flashes of reddish color caused by inclusions of hematite. Moonstone shows a glowing shimmer similar to labradorescence, but lacking in color. The display is produced from lamellar intergrowths inside the crystal. These intergrowths result from compatible chemistries at high temperatures becoming incompatible at lower temperatures and thus a seperating and layering of these two phases. The resulting shimmer effect is is called "schiller" or "adularescence", caused by a ray of light entering a layer and being refracted back and forth by deeper layers before it exits the crystal. This refracted ray has a different character than when it went in and produces the moonlike glow. Oligoclase is a member of the Plagioclase Feldspar Group. The plagioclase series comprises minerals that range in chemical composition from pure NaAlSi3O8, Albite to pure CaAl2Si2O8, Anorthite. Oligoclase by definition must contain 90-70% sodium to 10-30% calcium in the sodium/calcium position of the crystal structure. The various plagioclase feldspars are identified from each other by gradations in index of refraction and density in the absence of chemical analysis and/or optical measurements. All plagioclase feldspars show a type of twinning that is named after Albite. Albite Law twinning produces stacks of twin layers that are typically only fractions of millimeters to several millimeters thick. These twinned layers can be seen as striation like grooves on the surface of the crystal and unlike true striations these also appear on the cleavage surfaces. The Carlsbad Law twin produces what appears to be two intergrown crystals growing in opposite directions. Two different twin laws, the Manebach and Baveno laws, produce crystals with one prominant mirror plane and penetrant angles or notches into the crystal. Although twinned crystals are common, single crystals showing a perfect twin are rare and are often collected by twin fanciers.

Legends, Myths and Healing Properties:

MoonstoneMoonstone is believed to possess energy that is balancing, introspective, reflective, and lunar. It is capable of helping one with the changing structures of ones life on the physical, emotional, mental, and spiritual levels. It is a stone for hoping and wishing. It can be used to alleviate emotional tension and to enhance the positive attributes of creativity and self-expression. It cleanses negativity.