Gemstones I Love – the Feldspar Group
The Feldspar group includes several very popular gemstones – Amazonite, Moonstone, Sunstone, and Labradorite among others. In the earth’s crust, feldspars may be more abundant than all other minerals combined. The majority of the common feldspars fall into two groups, (1) the alkali feldspars – potassium aluminum silicates (KAlSi3O8) and sodium aluminum silicates (NaAlSi3O8) and (2) the plagioclase feldspars – combinations of sodium aluminum silicate (NaAlSi3O8) and the calcium aluminum silicate (CaAl2Si2O8). In some cases, the similarities and differences become difficult to interpret.
Sunstone is an interesting feldspar gemstone with a glittery appearance and usually an orange or reddish color, hence its name. The glitter effect is caused by inclusions of the mineral Hematite, or sometimes also Goethite or Pyrite. It can be translucent to opaque. It’s found in the US and Canada, in India, Madagascar, Russia, and also in Norway. Sunstone is best with flat surfaces or cut as a cabochon.
The optical effect appears to be due to reflections from inclusions of red copper, in the form of minute scales, which are hexagonal, rhombic, or irregular in shape. These inclusions give the stone an appearance something like that of aventurine, hence sunstone is known also as “aventurine-feldspar.” The optical effect called shiller and the color in Oregon Sunstone is due to copper. The middle part of this crystal sparkles, and usually the color is darkest in the middle and becomes lighter toward the outer edges.
The feldspar which usually displays the aventurine appearance is oligoclase, though the effect is sometimes seen in orthoclase: hence two kinds of sunstone are distinguished as “oligoclase sunstone” and “orthoclase sunstone.” Sunstones are believed to have metaphysical properties for crystal healing and gem therapy. The sunstone is linked to good luck and good fortune.
The color of moonstone varies from almost clear to white to yellowish translucent. Moonstone is generally cut as cabochons. This gem can be found in Myanmar, US, Brazil, India, Madagascar, and Sri Lanka. Moonstone has been used in jewelry for centuries, and was known and used in ancient times . The Romans admired moonstone, which they thought came from solidified rays of the moon. Both Romans and Greeks associated Moonstone with their lunar deities.
Moonstone became popular during the Art Nouveau period when French goldsmith René Lalique and many others created jewelry designs using this stone.
Moonstone is feldspar with a pearly and opalescent luster. Moonstone is composed of two feldspar species, orthoclase and albite. The two species are intermingled. As the newly formed mineral cools, the intergrowth of orthoclase and albite separates into stacked, alternating layers. When light falls between these thin, flat layers, it scatters in many directions producing the phenomenon called adularescence.
The most sought-after moonstones (nearly transparent and with a decided blue sheen) usually come from Sri Lanka. The earliest commercial mines were located in the Adula mountain range in Switzerland… whence came the name for its characteristic sheen, adularescence. The most common moonstone is of the mineral adularia. The plagioclase feldspar oligoclase also produces moonstone specimens. Deposits of moonstone occur in Australia, the Austrian Alps, Mexico, Madagascar, Burma, Norway, Poland, India, Sri Lanka, and the United States.
Rainbow Moonstone is technically a white labradorite. Although although rainbow moonstone and moonstone are in the same family, the two stones are geologically different. The rainbow moonstone is whiter than true moonstone and has the internal reflectance of labradorite. It was discovered in the 1960s and has become very popular.
This stone is thought to help in balancing the psychic centers and grounding negative energies. It helps you to accept the ups and downs of life and is specifically helpful at opening you to your spiritual gifts. All the various Moonstones are connected to water and to the lunar cycles. Rainbow Moonstone is thought to bring calmness coupled with awareness. It can also alleviate many degenerative conditions with respect to the hair, skin, eyes and fleshy organs of the body. It has been said to provide remedial action for disorders such as swelling, insect bites, bee stings, and anaphylactic shock.
Moonstone is connected strongly with the moon and intuition and empathy. The most powerful effect of moonstone is that it is calming to ones emotions. Rainbow Moonstone is wonderful at balancing yin and yang energies. It is especially good at helping males get in touch with their feminine sides.
Labradorite is an important feldspar gemstone and one of my favorites. It often displays a beautiful iridescent play of colors, which can move as the stone is rotated. Labradorite gemstones usually have a dark base color with metallic-looking color plays of blue, green, yellow, and red.
The display of beautiful iridescent colors is caused by internal fractures in the mineral that reflect light back and forth, dispersing it into different colors. This effect, known as labradorescence, gives Labradorite its appeal and fame. Specimens sold to collectors are usually polished or sliced by dealers to fully bring out this effect. Sliced slabs are sometimes sold by dealers in water, which enhances the effect.
Labradorite belongs to the Plagioclase Feldspar group, an isomorphous solid solution series. Albite is one member, containing sodium and no calcium. The other end member, Anorthite, contains calcium and no sodium. Labradorite is an intermediary member of this series.
Amazonite is a popular translucent to opaque blue green potassium aluminum silicate that can be found in Brazil, Madagascar, Russia, India, Kenya and in the US in Colorado. Specimens from Colorado are sometimes found with smoky quartz, orthoclase, and albite. When this combination occurs, the value of the specimens is much higher. The best green crystals have come from pockets in schist near Crystal Peak and at Pikes Peak, Colorado, and can be associated with smoky quartz. Good green crystals were found at Amelia, Virginia.
Amazonite has a Mohs hardness of 6-6.5 Amazonite crystallizes at a relatively low temperature as does Albite (a sodium feldspar) and these two are often found together in layers. Twin crystals are common and also a blocky habit. Microcline is a common potasium feldspar and Amazonite (KAlSi3O8) is the rare green variety of microcline. Its green color is thought to be due to trace impurities. Amazonite can display “schiller” a type of iridescence similar to Labradorite and Rainbow Moonstone. Schiller is an internal reflection from different planes within the crystals
This stone has been known and used for thousands of years. In Greek Mythology the Amazons were a nation of women warriors and this is may be a source of the name of this stone. It also may have been named for the Amazon river, although it does not occur near the river. The ancients called amazonite the stone of courage. It has also been thought to endow the wearer with hope and confidence. The best green crystals have come from pockets in schist near Crystal Peak and at Pikes Peak, Colorado, and can be associated with smoky quartz. Good green crystals were found at Amelia, Virginia, in Brazil, India, Russia, and Madagascar. Microcline feldspars are used in the manufacture of glass, enamel and porcelain products.