Properties of Turquoise

Properties of Turquoise

by Ashutosh Roy

The chemical name of Turquoise is Hydrated Copper Aluminum Phosphate. The chemical formula is CuAl6(PO)4(OH)8*5(H2O). According to the formula, it comprises of three primary ingredients Copper, Aluminum and Phosphorous. Turquoise has got occasional presence of Zinc, Iron and Chromium as impurities.

Turquoise – The Insight

Mother earth has stored marvelous treasures in her belly and Turquoise is one of the most precious stones that her sons have been digging out since 6000 BC. Aren’t you inquisitive to know all about it?

This modern yet one of the most ancient gemstone is said to be the result of nature’s whims. Before we delve deeper into its properties and attributes, lets understand clearly that Turquoise is not a primary mineral. It’s rather a collection of several minerals from the earth’s crust, formed under special weathering effects. The entire process is controlled by the nature itself to produce the ever-growing popular stone – the turquoise. A simple example will make it clear. As soon as Phelp Dodge had changed his way of extracting Copper ore, nature refused to produce Turquoise, due to the change in the weathering effect, in the same Tyrone mine, which had been producing turquoise for quiet some time.

The mother stone of Turquoise is called Matrix, which means Turquoise resides on the Matrix and is carefully cut as the method of extraction. The best colour dazzles when the colour of the matrix contrasts with the colour of the Turquoise. A thin and evenly spaced layer of Matrix, called Spider Web, eventually enhances the look and feel of Turquoise. As a secondary material, when meteoric or groundwater percolates through rocks that contain copper, Turquoise is formed. Copper may come from varied sources, which affect the quality and colour of the Turquoise. If Copper comes from Copper Sulphides, then it produces bluish shades and if Copper comes from carbonated malachite, the colour turns greenish. Now, if we look at its iron component, if it is from apalite, the colour becomes black, iron oxide produces golden-brown while rhyolite produces the yellow colour. If Turquoise is not cut carefully from the Matrix, impurities remain affecting its colour.

The chemical name of Turquoise is Hydrated Copper Aluminum Phosphate. The chemical formula is CuAl6(PO)4(OH)8*5(H2O). According to the formula, it comprises of three primary ingredients Copper, Aluminum and Phosphorous. Turquoise has got occasional presence of Zinc, Iron and Chromium as impurities. The presence of these impurities results in deviation from the elegant Turquoise blue colour. According to physical chemistry it belongs to the Class Phosphate.

As it belongs to the class phosphate, Turquoise is fragile and sensitive to solvents. The hardness of Turquoise ranges between 5 and 6, which is even lesser than a window glass. The hardness of a deeply mined turquoise is just above 2. That’s why Turquoise are always advised not to keep close to the other stones or other rough ornaments, which may result cracks in this auspicious stone. So, the rough and tough people should think twice!

Even Perfumes and other cosmetics may be detrimental, because of its super sensitivity to solvents. If you wear a Turquoise, be careful of your skin oil also. The “skystone” should not be exposed to direct sunlight. Heat is to be strictly avoided. But then how to maintain it? Cleanse it with a little warm water and dry it with some soft material like woolen clothes.

Various techniques have been evolved to increase its hardness and decrease its porosity. Light waxing and oiling enhances the colour and luster of Turquoise. This technique is widely used today to increase the durability of Turquoise. Some more technologies have come up today like “pressure technique” by water glass, epoxy and plastic to produce an artificial wetting effect to reduce the porosity.

Now lets take a quick look at the different colours of turquoises. Turquoise had first been found in Copper mines in Persia, which produced Sky Blue colour and the colour has become a symbol of reference and named as “Turquoise Blue”. The effect of Copper results the original blue colour. The variety in blue colour is a result of geographical location and other natural factors. Most of the Turquoise is concentrated near the copper-aluminum, and finally lands up in the iron or zinc-aluminum end. This natural phenomenon turns most of the turquoises to various shades of blue and green or bluish green and greenish blue. Some Turquoises have been found in Gold mines and Diamond Mines also. The presence of Iron and Chromium leads to Green colour. For example, Indian mines produce green colour turquoise due to the adequacy of Iron. Again, excessive heat can dehydrate the Turquoise to turn its colour to Green. Zinc changes the colour to yellowish but more importantly increases its hardness. Some Nevada and Tibetan Turquoise contain zinc.

Turquoise is opaque by its nature. The hardness of turquoise, measured by the Mohs scale of Physical Science, varies remarkably. The lower limit starts from 2 and the upper limit is 6. Hardness varies due to several natural factors like environment and its mother stone, matrix. The hardness also depends upon the processing or treating of Turquoise. Silicification process, which involves minute Quartz particles, increases the hardness to a large extent. Its softness makes it very difficult to use the gem directly by the Jewelers. Turquoises, which have not undergone the silification process, at the least, undergo stabilization treatment before being mounted on a necklace.

Properties at a glance

Associated Minerals Pyrite, limonite, quartz, chert, cuperite, manganese oxide, apatite, chalcopyrite, chalcedony, and clays
Birefraction 0.04
Chemical Formula CuAl6(PO4)4(OH)8*5(H2O),
Chemical Name Hydrated Copper Aluminum Phosphate
Class Phosphates
Cleavage None
Colours Mainly in shades of blue and Green
Crystal System Triclinic Bar 1
Crystal system Triclinic
Density 2.6 to 2.8
Fracture Conchodial
Luster Dull to Waxy
Refractive Index 1.61 to 1.65
Specific Gravity 2.60 to 2.80
Transparency Opaque

The best stones are almost natural but they are fragile and prone to color fading. But the nice look and the royal colour attract everybody. These stones are cut, shaped and polished to mount on your third finger.

As the popularity grows up, faking becomes an integral part. People have been faking for centuries. Fake turquoises are made up of ceramics, bone, colored minerals, celluloid, plastic etc. A hot pin will give out smell of resin from a synthetic turquoise. But, this is not the only kind; other faking methodologies may also deceive your eyes. So, you may prefer to visit Zach-Low Turquoise Museum, New Mexico, to test the Turquoise before investing your hard-earned dollars.

You may not be a student of Physics or Chemistry to comprehend all the properties in details. So what? Go ahead! After all, the taste of pudding is in the eating. So, why to restrain yourself from a glittering third finger with an original Persian Blue Turquoise before the next board meeting, which may turn your luck (!) also.