Monday, 25 August 2014

RUBY - The Undisputed King of Gemstones (Part-2)

One of the most important aspects of Gem Identification is the study of inclusions. It is the most fascinating and awe-inspiring experience when one gets to peep inside a stone and look at these marvelous inclusions. Inclusions can be described as a foreign element trapped inside a stone which can give one a clue about the origin, treatments undergone by the stone and it helps in distinguishing between natural stones and its synthetic counter parts.

This post is a continuation of the previous post, Ruby- the Undisputed King of Gemstones. This post will talk in detail about inclusions found in natural and synthetic rubies and its imitations.

Natural Ruby:
The characteristic inclusions of natural ruby include rutile silk which are elongated rutile crystals that give the appearance of needles. In ruby usually there are three sets of needles which intersect each other at an angle of 60°. The arrangement of these needles can cause a phenomenon in corundum, which is the creation of a star. Usually we get to see six-rayed stars and such stones are fashioned in cabochons.





RUTILE NEEDLES



RUTILE SILK



STAR RUBY

Similar looking needles are usually found in Garnets but they are coarser than the rutile needles present in rubies. Boehmite needles are also seen often in rubies.

Crystal inclusions are seen very commonly in rubies. Spinel octahedral crystals, zircon, haematite, calcite, apatite and mica crystals are often found in rubies. Two phase inclusions, three phase iclusions, color zoning – angular, straight and hexagonal are also prominent inclusions.
CALCITE CRYSTALS

ANGULAR GROWTH MARKS

Burma rubies usually display the characteristic silk and apatite and calcite crystals. Fingerprint like inclusions are also common. Thai rubies on the other hand lack the silk in them, instead they have boehmite needles. Color zoning is also a prominent clarity characteristic. Mong Hsu rubies usually tend to have dark cores and they are treated for improved appearance.

COARSE BOEHMITE NEEDLES



FINGERPRINT INCLUSION

Treatments:
Most of the rubies undergo treatment to improve their color and thus marketability. The most common treatment followed worldwide is heat treatment, wherein rubies are heated in furnaces at particular temperature. With the help of this treatment not only the color improves but also the inclusions which affect the clarity of the stone become less visible. But the treatment causes distortion of inclusions. Characteristic inclusions after treatment are-
  • Discoid fractures which result from expansion of crystals due to heat. These are tension fractures with a healing rim.
  • Clouds formed by melting of rutile silk.
  • Broken silk. (these give the appearance of dotted lines)
  • Snowball inclusions caused by melting of crystals.

BROKEN SILK


DISCOID FRACTURE



SNOWBALL INCLUSIONS

In addition to heat treatment sometimes, flux is filled into the fractures to improve the appearance of rubies. When these kinds of rubies are examined under the microscope glassy flux like substance can be seen. 

In other cases dyes are filled into the fractures to improve the color. But sometimes a stone might not have fractures but a poor color, then cracks or fractures are created by rapid heating and cooling and then the dye is introduced. This process is called Quench Crackling.

QUENCH-CRACKLED RUBY


Lattice diffusion is another method in which the stones are exposed to  high heat and chemicals to diffuse another element into the stone which can result in improved appearance. It is usually carried out for stones which do not produce effective results from heat treatment. Lattice diffusion is carried out with two elements chromium and beryllium. Chromium gives rubies a lighter coat of red color whereas beryllium gives them deep orangy red color.

Synthetics:
A synthetic gem can be described as gem which is grown in a laboratory and has the same crystal habitat and chemical composition of their natural counterpart.
Laboratory made rubies are also widely available in the market. It is important for a gemologist to have clear understanding of the various processes used for creating these rubies and how to separate them from their natural counterparts.

Flame Fusion: under this process the powdered chemicals are dropped on a flame and are melted at high temperatures and then left for crystallising. The crystallised mass is termed as boule. Many stones can be cut out from a boule. It is the most commercially viable method of synthesising gems. Typical clarity characteristics of this method are:
  • Presence of gas bubbles
  • Curved growth marks (curved striae)
  • Somewhat an unnatural appearance (mainly uniform color)

CURVED STRAIE AND GAS BUBBLES

FINGERPRINT INCLUSION

Pulling: this method is similar to the flame fusion method. The only difference is that this process uses a template crystal which helps in providing a basic structure for the growth of the synthetic material. The template crystal is attached to the rod which touches the molten chemicals and it pulls out some melt with it. The melt crystallises forming a boule.

Flux Growth: this process is most widely used for producing synthetic emeralds but synthetic corundum is also produced using this process. Here in a crucible, usually made of platinum (to avoid corrosion) is used and flux is filled in. Template crystals are immersed in the liquid chemicals. Crystallisation process takes a long time, sometimes a year also. The cost of production is very high in this method as the equipment is very expensive and the period of production is very long. This process produces characteristic fingerprint inclusions which look very similar to the natural ones.
SYNTHETIC FLUX RUBY

Hydrothermal process: under this method the manufacturers try and replicate the conditions that exist in the structural layers of earth for gem formation. In big containers powdered chemicals are put at the bottom and then they are subjected to high heat and pressure. These containers are filled with water which again is subjected to very high heat and pressure. As the chemicals dissolve they rise where the water is slightly cooler and this is where the crystallisation takes place. Liquid inclusions are usually present in hydrothermal rubies.

Imitations: these can be termed as just mere look alike of a natural gemstone. Imitations can be classified into two categories:
Assembled stones
Look- alike –gems
Assembled stones are prepared by combining two or more different materials. The most common assembled imitations are-

Glass and garnet doublet- the top is usually made of almandite or pyrope- almandite garnet and the base is a glass. The top shows natural inclusion of a garnet and the bottom will show gas bubbles. The separation plane is above the girdle.
GLASS AND GARNET DOUBLET


Synthetic spinel triplet: top and bottom of synthetic colorless spinel and at the girdle is colored cement.

Sapphire and synthetic ruby doublet: top is natural green or blue sapphire and bottom is synthetic ruby.
SAPPHIRE AND SYNTHETIC RUBY DOUBLET

Look-alike-gems: there are many gems which look like natural rubies. Gems like spinel, red garnet, synthetic cubic zirconia and quench crackled quartz.
QUENCH CRACKLED QUARTZ

RED SPINEL

RED SYNTHETIC CUBIC ZIRCONIA

These two combined posts of ruby take us through each and every important aspect and provide the fundamental knowledge about the prized gemstone.
Ruby is a gem which holds the highest position among all other gemstones. Its rich, vivid color leaves one speechless. One can’t help but admire nature’s this awe-striking creation and that is why it is termed as the Undisputed King of Gemstones.



*The Author is a Colored Stone Graduate from Gemological Institute of America, Mumbai and a Diamond Graduate from Solitaire Diamond Institute, Bangalore. She also holds a Diploma in Jewelry Designing & Manufacturing from Jewelry Product Development Centre, Jaipur. She also blogs at 'The Jewel Affair'

*Picture Courtesy: Google Images