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History & Introduction


Moonstone is a popular variety of gemstone of orthoclase feldspar, a potassium aluminum silicate. This gemstone is from transparent to opaque oligoclase, which is a variety of plagioclase albite and sheet mica. Moonstone gemstone is famous for the display of a distinct sheen under certain conditions related to lighting, and it is the sheen that renders the stone as one of the most remarkable gemstones available at present. In fact, its name is owed to the almost magical, bluish white shimmer it shows that closely resembles as of the moon. Gemmologists refer to the shimmering phenomena as 'adularesence'.

In India it is a sacred stone for the lovers, and is even known to be a "dream stone" that brings beautiful dreams. Sometimes in Arab countries women do wear moonstone gem for fertility purposes. It was even believed to be particularly protective to seafarers, who have used it since ancient times. In the time of full-moon, moonstone is very powerful for unification of love - and when the moon decreases, is believed to allow one to predict the future.

The effect related to optical of adularesence is because of unique structural pattern of moonstone. Albite with tiny inclusions and sodium aluminium silicate are intermixed with host rock layers of orthoclase, a potassium aluminum silicate. Lamellar (scaly) structure is formed with the alternating layers of different feldspars, which causes the interference of light as it enters the stone. Thin layers of alternating silicates lean to refract more attractive and colourful sheens, while thick layers of silicates produce less attractive, from white goes with colourless sheens. When light enters the stone, it gets refracted as well as scattered, which produce a very unique and attractive play of both light and colour. With moonstone, the aura of light actually look in to glow from deep within the surface of the stone. Moonstone was very famous during the time of "Art Nouveau" that took place more than 100 years ago. It was used in the making of jewellery created by the famous French Master-Goldsmith, René Lalique, and other contemporaries of his time.

Recognise - Moonstone gems are identified with the presence of adularesence. Other gems with a look that is alike do not have the phenomenal presence of adularesence that makes identification of moonstone is very easy. Moonstone gem consist of a composition of potassium aluminum silicate and is easily identified. Testing for hardness is frequently taken as the easiest methods for distinguishing moonstone from other materials. Other similar gems like opal, ammolite or chalcedony are significantly harder or softer than moonstone. High quality moonstone shows an incredible "three-dimensional" depth of colour that no other gemstone can imitate, forming a moonstone almost unmistakable.

Availability - The deposits of moonstone are often found as constituents in feldspar-rich granitic and syenitic pegmatites across the globe. Still maximum moonstone deposits are from India and Sri Lanka. Other important sources of deposits are Germany, Australia, India, Brazil, Myanmar (Burma), Switzerland, Madagascar, Tanzania, Mexico, Norway, and the United States. Sri Lankan moonstone is most famous because of the attractive blue colour material, however blue moonstone is becoming rare with time. India is famous to produce fine 'rainbow moonstone'. Switzerland's Adula Mountains gives the maximum interesting moonstone mines.

Buying Guide

Color - Naturally, moonstone is colourless, however it is available in a wide variety of colours that includes yellow, grey, mocha brown, pink, orange, green, blue and white. Many times it shows a white to bluish-white sheen, however other sheens can occur such as silvery and blue-orange. The moonstone from Sri Lanka is in pale blue sheen on a near-transparent body are the most precious one. India's moonstones exhibit a cloudlike plays of light and colour that are very precious that includes orange, beige brown, simple brown or green. Colours that are rare are smoke, blue, champagne, peach, red and black.

Clarity and Lustre - The clarity of moonstone naturally is available in translucent. Transparent specimens are not available in general, however it is unheard of. Transparent moonstone is the most precious one. Moonstone possess an attractive vitreous to pearly lustre once it is cut and polished. Some moonstones shows chatoyancy. These are known as 'cat's eye moonstone' during trade. With the asterism effect we get the other rare varieties of moonstone. They are related to 'star moonstone'. Cat's eye and star moonstones are remarkably rare and highly in demand.

Cut and Shape - Moonstone is always cut into en cabochon to maximize the required effects of adularesence. The orientation of the cut with moonstone is very important. It is essential to show the peaked light reflection along with a genuine height of the stone that is why most moonstone is cut with a high dome. The crystal axis must locate precisely by the cutters in the zenith of the stone in order to get the perfect orientation resulting in m the maximized schiller effects. Very often the moonstone gives the cut in oval shapes since ovals tend to preserve the maximum weight in carat. There are some faceted stones that are highly transparent, however faceted moonstone is very rare.

Treatment - Moonstone is not treated or enhanced in any way, still there are reports of bright blue moonstones that is 'coated' for colour-enhancement.

Gemmological Characteristics:

Chemical Formula KalSi3O8, Potassium aluminium silicate
Crystal Structure Monoclinic, prismatic
Colour pale sheen, colourless, yellow
Hardness From 6 to 6.5
Refractive Index From 1.518 to 1.526
Density From 2.56 to 2.59
Cleavage Perfect
Transparency From Transparent to translucent
Double Refraction or Birefringence -0.008
Lustre From Vitreous to pearly
Fluorescence Weak; bluish, orange
Mineral Class Orthoclase, Oligoclase, and other members of the feldspar group

Classification:

  • Cat's Eye Moonstone - Moonstone exhibiting chatoyancy.
  • Rainbow Moonstone - Moonstone with a blue sheen. It can also referred to Labradorite.
  • Star Moonstone - Moonstone displaying asterism.