Feldspar Gemstones - A huge family of minerals
Introduction
Feldspars belong to a huge family of minerals, which are the most prodigious on earth. Apart from gemstones, feldspars are used in the making of bathroom tiles, and their fine and ground forms are used in making cleaning materials. Though these may seem menial uses for these minerals, there are some which are so beautiful that they are some of the most demanded gemstones on the planet.
The main use of feldspars does not make for a very glamorous purpose, but you should bear in mind that some of the most expensive gemstones on the planet are also used to do some menial jobs; diamonds are also used in the cutting of glass. Mother Nature is a wondrous creator and given time, pressure and temperature, She can turn the most common types of minerals into wonderful gemstones, and some of these end up being the most beautiful, rare and valuable gemstones.
The Earth’s crust has a high percentage of feldspars, but once in a while, they are found as some of the most glorious of gemstones. The gemstones that are made from feldspar minerals produce some of the most scintillating effects that are ever known to Man. This is something that is normally seen in the beryl family of gemstones, which derive their colors from mineral impurities which are found in their crystal structure. This is the reason why these types of gemstones are known as allochromatic gems.
Gemstone bearing feldspars usually form within veins of molten magma, and this is the reason why they are normally found in intrusive and extrusive igneous rocks. Igneous rocks are those which are formed by the solidification of molten magma. Feldspars can also be found growing in metamorphic rocks. Metamorphic rocks are those which were already formed and they change when they are re-heated or exposed to other rock-changing elements. These gemstones are also found in sedimentary rocks.
One thing to note is that all gemstones in the feldspar family have a cleavage that occurs in two directions, and one of them is always perfect. The name feldspar comes from two different German words. The first is Feld, which means field, and the other is Spar, which is a name given to all gemstones that have a perfect cleavage.
The perfect cleavage is the one that is responsible for the beautiful schiller effect. This is a type of iridescence; a glorious display of colors deep within the structure of the crystal. This effect is brought about by the interference of light passing through the microstructure of the feldspar gem. One of the feldspars, Sunstone, displays this iridescence in the form of a silvery aventurescence. There are other gemstones that are included in this family, and these are Moonstone, Labradorite, which gives a schiller effect that is so unique that it is called labradorescnce. Albite, Orthoclase and Adesine are other members of this gemstone family.
A profile of Feldspar gemstones
There are many places, all over the world, where feldspars are found, usually in pegmatite and meteorite rocks. They are found in all ore-forming and rock processing processes, which include hydrothermal, sedimentary, igneous and metamorphic processes. However, only rarely are feldspars found as gemstones. These are some of the most diversified minerals on the planet and they are thoroughly investigated. However, it is not until recently that they got the attention that they truly deserve as gemstones. These minerals did not command any attention until the middle of the 18th Century, when a writer called Wallerius wrote about them in his book, ‘Mineralogy’, which was published in 1753. In his book, he describes them as varieties of a ‘spar dense and lustrous’. And they are distinguished by having wonderful colors of red, gray and white. It was during the same period that scientists started to truly investigate feldspars through crystallographic and chemical analysis. Today, there have been at least 40 types of feldspars that have been identified, and all of them have distinctive features and fantastic colors.
Depending on their chemical structure, feldspars have a specific gravity that ranges from 2.5 to 2.7. They also have a hardness that ranges from 6. 6.5. Feldspars, on the other hand, have a fracture that occurs along two different cleavage planes, and one is usually perfect. The cleavage is subconchoidal to uneven in nature. Most feldspars are said to form from the crystallization of molten igneous rocks. They have a crystals structure that is flattened, tabular and twinned in a complex manner.
There are certain physical characteristics that can be attributed to all feldspars. One is that they have two distinct and developable cleavages and one is perfect, and is called the basal plane. On this plane the luster is seen as a pearly color, and the cracks of the cleavage produce a brilliant iridescence effect when light is reflected off them. The other cleave, which is not perfect is found running parallel to the pair of faces, which end in the acute edges of the crystal prism. You will find a lot of similarity between the cleavages of monoclinic and triclinic feldspars, with just one different feature: The monoclinic feldspars have cleavage planes which run at perpendicular angles. This is the reason why these minerals are called Orthoclase, which translates to ‘cleaving at right angles’. The triclinic feldspars have cleavage planes that are not exactly at right angles. This is the reason why they are called Plagioclase, which means ‘cleaving at oblique angles.’
The Schiller effect portrayed by feldspars is due to the presence of lamellae, which are actually thin, platelet-like layers that occurs within the crystal structure of the gem. This is a type of iridescence that is brought about by the scattering of light as it passes between these lamellae. The Chiller effect is best seen in Labradorites, and this is seen as a display of lovely colors ranging from gold, yellow, blue and green. The colors can be described as homogenous, but they can also vary depending on the individual crystal. There is research going on to see if the low quality feldspars that have been found in Arizona, can be treated using Gamma rays, in order to improve them, making them gemstone quality minerals. As the research continue, the possibility is very likely.
The most common feldspar gemstones
Amazonite
This is a gemstone with a triclinic crystal system and has a hardness of 6 on the Mohs scale. It has a light green, blue or bluish-green color that is mottled in appearance. Sometimes the colors crisscross in a fine network of light striations. It is this feature that helps in distinguishing Amazonite from the beryl or jade gemstones of the same color. In the beginning, the gemstone was called the Amazon stone, since it was mainly found around the Amazon River. This is a term that was also used to describe Nephrite. Amazonite is formed in metamorphic rocks, pegmatite and intrusive magmatic rocks. Some of the finest amazonite gemstones are seen at the Amelia Courthouse, in Pikes Valley, Virginia, in the Unites States of America. In Colorado, you find a unique type of amazonite which are large in size and have smoky quartz crystals, and are found in cavities formed out of coarse pegmatite granite. Amazonite is a favorite gemstone among gamblers, since it is said to attract good luck, and they think that they will win more money with the gemstone on their bodies.
Labradorite
This is another feldspar with a triclinic crystal system and a hardness that varies between 6 and 6.5 on the Mohs scale. Yellow, green and blue are the most common colors of this gemstone, but at times it is found in copper-red, but this is very rare. You will find the best quality of labradorite, which also happens to be the most magnificent of all feldspars, on the Coast of Labrador in Canada. The gemstone is usually found in a very shady dark gray color, and one would frown upon its importance in the feldspar family. However, this is a gemstone that has a very brilliant display of colors, and the occasional and unexpected flash of light. These two features combine to make it a very special gemstone.
Labradorite is a feldspar found in lime-soda, and is made up of 25% alumina and 55% silica. It also has 2% iron oxide, 4% soda, 11% lime and a small amount of potash. It is the feldspars that have this chemical composition that truly belong to the labradorite variety. They are found in Labrador, The United States, Madagascar and Scandinavia.
This is a gemstone that is never faceted since this would interfere with the display of reflected light. They are normally cut as flat gemstone or sometimes with a light convex curve. The cutter must make the cut to be parallel to the reflecting planes or there will not be any play of color. This is a gemstone that has sudden and short displays of unexpected colors, and this is the feature that is most striking about it; this feature is now known as Labradorescence.
In Russia, there is one peculiar labradorite which display a figure that can be recognized as the image of Louis the 16th. The head, which stands out from a background of gold and green, is made of the finest azure-blue labradorite. On the top, it has a beautiful crown of garnet red colors and a rainbow border. It also has a silvery, shiny plume. The owner of this remarkable piece was paid 250,000 million francs for it in 1799; this was quite a fortune at the time. During this period, labradorite was used in creating objects that had a metallic color as well as iridescence; they were mainly used in making butterfly wings. At the start of the 19th Century, it was very popular to make reliefs of Mandrill Baboons out of labradorite. It was also used in coloring the counts of some of the most beautiful animal creations.
This is a gemstone that is found widely all over the United States of America, and is found in Lewis and Essex counties in New York. It is found naturally as boulders in the glacial deposits found here. The boulders can be found all the way down to New Jersey and Long Island. The stones were found in abundance along one of the rivers in Lewis County, to the point that it is called the Opalescent River. There are large quantities of labradorite mined in Keeseville New York and are used for making monuments and in building. Labradorite can also be found in Arkansas, New Jersey, and Pennsylvania. However, those that are used in the making of gems are found in Finland, and Labrador, Canada. Many centuries ago, Labradorite was said to have good luck, but in recent times, it is mainly popular among New Age followers, who consider it to be spiritual and to have psychic-enhancing abilities.
Moonstone
This is a gemstone that has a monoclinic crystals structure and a hardness of 6 on the Mohs scale. It is an almost colorless gemstone that has a tinge of yellow, white or silver, with a blue shimmer on the surface.
The name moonstone was given to this gemstone because it has a colorless, translucent and almost perfect clarity. When viewed from certain angles, this gemstone displays a milky, blue light, which can be compared to the light given off by the moon. Other names have been used to describe this gemstone, and these include Fish Eye, Wolf’s Eye, Water Opal, Ceylonese Opal and Girasol. It is common to use very fine glass imitations of this gemstone in the designing of expensive jewelry. The fakes are less hard, but much denser than Moonstone, and they only refract in one direction, whereas moonstone is said to refract light in two directions.
The finest moonstone specimens are found in Sri Lanka, and it is so popular that it has been designated as the national stone of the country. Miners normally dig very deep and narrow holes in the ground in order to collect these gemstones. They commonly lower themselves into these narrow pits using ropes, then they fill wicker baskets with gravel and loose dirt, before hoisting these to the surface. At the surface, the gravel and dirt is washed by hand, and the gemstones selected from the cleaned gravel. The finest specimens of moonstone in North America come from Allen’s Mica Mine, which is found in Amelia Courthouse in Virginia.
The myths surrounding moonstone include the power to counter the negative influence of the number 13. People also used to hang moonstone amulets on trees so they could bear abundant fruit. This gemstone was also said to help people who have epilepsy, insanity and those whose minds tended to wander off. The gemstone was also said to help reconcile lovers and also increase physical strength. When a moonstone was placed in the mouth, it was said to help in sorting out sensitive matters. This is a gemstone that was also used for hypnotic purposes. In the Orient, it was said to turn the rays of the moon into solid matter. It is said that the light in the moonlight was actually a living spirit which is found in the stone. When it is sometimes viewed using a microscope, there is a peculiar flaw that resembles a centipede that can be clearly seen.
Noble Orthoclase
This is another feldspar with a monoclinic crystal structure, and a hardness of 6 on the Mohs scale. It has a medium to deep yellow color and is completely transparent with a luster that is vitreous in nature. This is a gemstone that is mainly faceted using the Step-Cut and most specimens do not have any inclusions at all. This is a very rare type of orthoclase, and for this reason, it is sometimes classified as valuable. This is a gemstone that is a favorite among connoisseurs and collectors and is hardly known to the casual gemstone buyer. Noble orthoclase is mainly found in Madagascar within pegmatite rocks.
Sunstone
This is a feldspar that has a triclinic crystal system and a hardness of 6 to 6.5 on the Mohs scale. Most of these gemstones have a white to straw-yellow color, but there are a few exceptions which have a red and/or green color. They have a pale to intense density of color and sometimes have areas that have red, green, schiller or all three at the same time. The schiller effect on these gemstones comes from thin and very thin platelets which are dark brown or opaque in color. Within the crystals, these platelets look like pink structures but as you come towards the surface, they seem to be whitish or metallic in color.
These stones are transparent and have a gem quality; they were also thought to have metallic copper at one time. There are slim scales of hematite that are found in planes that are parallel to the direction of the cleavage, which is perfect in nature. The reason why this gemstone has a glittering sheen is the way in which light is reflected from the brilliant surface of these scales; it is usually red in color. At the start of the 19th century, the sunstone was very rare and the price it was accorded was also high. To this day, there are only a few small specimens that have been known and these were found on Sattel Island in the White Sea.
Sunstone is found in Siberia, Norway and Statesville, North Carolina. It is also common in the Basalt flow which is near the Rabbit Hills of Lake County in Oregon. There is a rare type which is mined in Media, Pennsylvania.
There are no myths of folk stories that can be found regarding the sunstone, even from ancient times. However, New Age devotees say that the gemstone has protective abilities. It has been claimed to give more physical strength, especially hen the wearer is going through stress or has an illness.
In summary
Feldspar is quite a fascinating mineral family, given its chemical make-up, colors and light habits. When used for its most mundane of purposes, it is used for the making of the abrasive particles in toothpaste. In its most high function, a feldspar can be faceted into the most fascinating of gemstones. It is both sublime and simple. According to Ralph Waldo Emerson, A man is quite alike to the Labrador Feldspar, which seems to have no luster when you place it in the palm of your hand, but when you come across a certain angle, then you see the deep and beautiful colors within. This is quite an interesting family of gemstones, which are not very common but are very valuable. When you think about it, this can be said to be the most sublime, but fascinating group of gemstones ever.
