Moonstone/Oligoclase from galleries.com

Chemistry: Na(90-70%) Ca(10-30%) (Al, Si)AlSi2 O8, Sodium calcium aluminum silicate.

Class: Silicates

Subclass: Tectosilicates

Group: Feldspars

Uses: ornamental and semi-precious stone and as mineral specimens.

Specimens

Oligoclase is not a well-known mineral but has been used as a 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 separating and layering of these two phases. The resulting shimmer effect is 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. Moonstone is an alternate birthstone for the month of June.

Oligoclase is a member of the Plagioclase Feldspar Group. The plagioclase series comprises minerals that range in chemical composition from pure NaAlSi3 O8, Albite to pure CaAl2 Si2 O8 , 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.

PHYSICAL CHARACTERISTICS:

Color is usually off-white or gray or pale shades of green, yellow or brown.

Luster is vitreous to dull if weathered..

Transparency crystals are translucent to transparent.

Crystal System is triclinic; bar 1

Crystal Habits include blocky, or tabular crystals. Crystals have a nearly rectangular or square cross-section with slightly slanted dome and pinacoid terminations. Twinning is almost universal in all plagioclases. Crystals can be twinned according to the Albite, Carlsbad, Manebach and Baveno laws. Oligoclase can be found as a major rock forming component in granites and syenites.

Cleavage is perfect in one and good in another direction forming nearly right angled prisms.

Fracture is conchoidal.

Hardness is 6 – 6.5.

Specific Gravity is approximately 2.64 – 2.68 (average)

Streak is white.

Associated Minerals are quartz, muscovite and K-feldspars.

Other Characteristics: index of refraction is 1.533 – 1.552. Lamellar twinning may cause a grooved effect on cystal and cleavage surfaces that appear as striations.

Notable Occurrences include Sri Lanka; New York, USA; Russia; Sweden and Canada.

Best Field Indicators are occurrence, twinning striations, shimmer, density and index of refraction.

All About Rainbow Moonstone & It’s Hidden Powers from lakaiser.com

Rainbow moonstone.. such a magical stone! The name ‘Rainbow Moonstone’ was given due to the gemstone’s white sheen color that changes if it is rolled or rotated. The iridescent flashes on the gemstone have captivated the hearts of jewelry lovers for centuries. Moonstone is a mineral of the feldspar group and the optical phenomenon that causes the color play is known as Adularescence. The light moves across the gem much like the moonlight glides over a large body of water hence causing the extraordinary glow. The light reflects off of the thin layers of the feldspar minerals within the moonstone. The layers act as a diffuser, hence softening the light and allowing it to bounce around.

With its otherworldly facade, moonstone has mesmerized people of different cultures. Its use can be traced back to the ancient civilizations. The Romans believed that the moonstone was born from the solidified rays of the moon. The Greeks and the Romans have long associated the gem with their lunar gods. Other cultures strongly coveted that the stone’s powers were with the moon. It was especially prized during a full moon.

Although the Rainbow Moonstone found its way into jewelry throughout history, it wasn’t until the early 1900s that the stone became an iconic focal point. Rainbow Moonstone became immensely popular with various artists and goldsmiths during the Art Nouveau period, in the early 20th century. In the preceding years it was mainly used as an accent stone. Artisans like René Lalique focused on using natural, mystical stones with unique properties which were favored over glitzy stones. But the movement was short lived and it was soon followed by Art Deco which emphasized on the use of diamonds and precious gemstones. It wasn’t until the late 1960s that moonstone came back into fashion.

Seen as a veiled spectacle of light passing over the moon, the gemstone is highly valued among the monks, shamans, spiritualists, and devotees from various religions. The pearly iridescence it showcases holds a deep meaning and has a towering significance.

As ancient as the moon itself, the meaning of the Rainbow Moonstone lies within its playful glimmer. Its power nourishes, gives passion and awakens your feminine energies. The gemstone has the ability to not only heal you but is believed to guide you to your inner path. With the waxing and waning of the moon, it evokes tranquility and peace that has a sensual, enigmatic feel to it. It emanates an exuberance that can re-energizes a person’s mind, body and wash the negativity away. Enveloped in gleaming rays of gold, blue and purple the Rainbow Moonstone is embraced with white energy that makes it a protective gem.

But what does it really mean?

Often connected to the water signs, the Rainbow Moonstone is associated with lots of healing properties :

Enhances intuition

Makes wearer more accepting of change

Alleviates fear associated with change

Balances emotions

Promotes a calm mood

Encourages peace, harmony, and balance

Improves confidence

Helps a person become more passionate

Often called the “visionary stone”, Rainbow Moonstone mostly occurs in the regions of Armenia, Australia, the Alps in Austria, Mexico, Madagascar, Myanmar, Norway, Poland, India, Sri Lanka and the United States.