Inorganic Gemstones

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EDXRF

  • EDXRF is purely a surface analysis and is used to determine the bulk chemical composition of the sample surface area seen only in the X-ray region.
  • Different energy sources maybe used an X-ray tube or an electron beam.
  • A multi-channel analyser is used which gives a complete spread and separation of the wavelengths which is observed as a definite line spectra and expressed as kev / counts.
  • Depending on the element to be measured, different filters are utilized.
  • Elemental percentages are calculated using compatible software.
  • The spectrometer analyses elements which have a higher atomic number than 11. The lighter elements i.e. below Sodium (atomic number 11) cannot be detected. Since beryllium cannot be measured, a distinction between corundum and chrysoberyl cannot be made.
X-rays and Their Uses

X-rays have a wide application in gemstone identification.

  • X-rays are high frequency electromagnetic rays.
  • They possess the ability to pass through a substance which is normally opaque to ordinary light.
  • The greater the atomic mass of a substance, the greater is its opacity to the rays. E.g. carbon, oxygen, nitrogen have low atomic masses and are more transparent to X- rays while iron, calcium, zirconium which have higher atomic masses are less transparent to the rays.

X-rays are used in gemstone identification as follows:

  • Fluorescence: Gemstones exhibit fluorescent effects. E.g. Diamonds exhibit varying luminescence; Natural Pearl is generally inert while cultured pearls give a greenish yellow fluorescence, due to the presence of manganese. This is also observed in all freshwater and some Australian natural pearls and is therefore not conclusive.
  • Transparency: This is useful while examining complete pieces of jewellery e.g. in a pearl, transparency of conchiolin differs from the calcium carbonate pearl structure and therefore presents a distinctive appearance. Gemstones with heavier elements will be more opaque to X-rays, as is seen in synthetic cubic zirconia when compared to the transparency of diamond. Composite stones would present varying transparencies in the different portions.
  • Diffraction: X-ray diffraction is useful in identifying crystal structure (powder diffraction) and the analysis of the Laue diffraction patterns (spot pattern) in identifying the gemstone. Diffraction patterns are distinctly different for natural and cultured pearls. Natural pearls have a radial structure made up of aragonite crystallites while cultured pearls contain a bead nucleus surrounded by aragonite crystallites. A narrow X-ray beam is passed through the pearl in at least two directions. A hexagonal spot pattern in all directions is seen in natural while a hexagon and a square pattern in two different directions (90° to each other) is seen in cultured pearl.

Did you know?

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In Germany, the garland of ambers is hung around the necks of the infants, so that their teeth might come out without much trouble.

In Turkey, people fix a piece of amber in the hubble-bubble, dogged by an age old belief that the presence of the jewel would destroy all the germs and no disease would spread, even after many have dragged their puffs from it.

In Greece, people think if wine is poured into the cups made of amethyst, one does not get drunk after drinking that.

In Rome, a talisman having coral pieces is considered very auspicious to quell the bad spells of evil look. The Romans were in the habit of hanging chains made of ancient coral pieces from the cradle of the infants to protect them from evil effects.

In China, people wear rings studded with tiny conch or oyster shells as they believe it cures all aches such as stomach ache, worms and like.

In India, pendants made of silver and studded with pearls are hung from the necks of the children to save them from any bad effects.

Greeks still believe, if women wear blue sapphires then no sense of immorality would pollute their mind nor can any fear of the supernatural can trouble them.

The Pope Innocent III had circulated an order asking all the priests wear blue sapphire, so that morality can be strengthened.

It is said about turquoise, that when the stone changes its color into yellow, it actually signals bad times to the person who wears it.

It is believed that a turquoise gifted to a friend or a lover turns his or her life into one of happiness and good luck.

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