Corundum

saf-ahyuh r

Corundum Classification
Common Name Corundum
Species Corundum
Corundum Optical Properties
Transparency Transparent - Opaque
Refractive Index 1.767-1.772
Birefringence 0.008-0.009
Optic Character Uniaxial
Pleochroism Unobservable
Corundum Characteristic Physical Properties
Hardness 9
Streak White
Specific Gravity 3.98-4.1
Luster Adamantine, Pearly, Vitreous
Fracture Irregular/Uneven, Conchoidal
Cleavage None
Corundum Chemistry & Crystallography
Chemical Formula Al2O3
Crystal System Trigonal
Chemistry Classification Oxide

Corundum Spectra

Corundum Spectra
CORUNDUM DOUBLET (ε ray)

While in the same position the paler color of the e-ray can be seen by a 90 degree rotation of the polarizing filter, placed in front of the slit or eyepiece of the spectroscope. In this case the band in the green has narrowed considerably and the fluorescing doublet is less intense. Transmission of some green and blue has increased but the lines are again vague. Violet is absorbed as in all chromium spectra.

Corundum Spectra
CORUNDUM - RED DIFFUSION TREATED. (Unpolarized)

Chromium has been added by diffusion. The resultant chromium spectrum is fairly weak with no emission doublet seen in the deep red. The lines in the blue are vague and the central absorption band in the green is less intense compared to a untreated ruby of this color

Corundum Spectra
CORUNDUM - RED DIFFUSION TREATED (ω ray)

Chromium has been added by diffusion. The resultant chromium spectrum is fairly weak with no emission doublet seen in the deep red. The lines in the blue are vague and the central absorption band in the green is less intense compared to a untreated ruby of this color. Isolating the o-ray by means a polarizing filter increases the width of the absorption band in the green but not to the extent expected in a ruby of this color

Corundum Spectra
CORUNDUM - RED DIFFUSION TREATED (ε ray

Chromium has been added by diffusion. The resultant chromium spectrum is fairly weak with no emission doublet seen in the deep red. The lines in the blue are vague and the central absorption band in the green is less intense compared to a untreated ruby of this color. The absorption in the green has narrowed it has become very weak in this vibration direction compared to a ruby of this color.

Corundum Spectra
CORUNDUM DOUBLET (Unpolarized

Color due to chromium. The green sapphire crown on this doublet is too thin to be detected in the spectrum. The result is a typical chromium spectrum from the lab created ruby pavilion with the fluorescence lines in the deep red and absorption lines in the blue. The absorption band in the green is of moderate width. As in all chromium spectra the violet area is totally absorbed

Corundum Spectra
CORUNDUM DOUBLET (Unpolarized

Color due to chromium. The green sapphire crown plays little or no part in the main body color of this stone but can influence the absorption spectrum. The synthetic ruby pavilion provides the chromium spectrum with the broad band in the green and a weak fluorescing doublet in the deep red. The lines in the blue are weak and diffused probably due to a slight absorption in this area because of the iron content in the green sapphire crown

Corundum Spectra
CORUNDUM DOUBLET (Fluorescence spectrum

As we adjust the lighting to enhance the fluorescence in the red, the doublet at 694/693nm. dominates the spectrum accompanied by two others at 668nm. and 659nm. Weak areas of green and blue seen here are due to a small amount of light reflected from the facets of the stone entering the spectroscope

Corundum Spectra
CORUNDUM DOUBLET (Fluorescence spectrum)

Adjustment of the light path can pick up stray light scattered from within the stone. Intensity of this light is weak compared to that which is directly transmitted. However, any fluorescence lines can be detected as a contrast in the red area. As is expected from the synthetic ruby pavilion of this doublet the fairly strong fluorescence lines are seen in the doublet at 694/693nm. with the weaker ones at 668nm and 659nm

Corundum Spectra
CORUNDUM DOUBLET (ω ray)

Color due to chromium. The green sapphire crown on this doublet is too thin to be detected in the spectrum. The result is a typical chromium spectrum from the lab created ruby pavilion with the fluorescence lines in the deep red and absorption lines in the blue. When viewed with a polarizing filter, the central absorption band is now stronger and broader to cover more of the orange and green areas. The fluorescing doublet is seen to strengthen in intensity and the lines in the blue appear a little more vague.

Corundum Spectra
CORUNDUM DOUBLET (ω ray)

When viewed through the crown any dichroism is difficult to detect due to the different orientation of the optic axes in the two sections of this composite stone. To see maximum contrast the stone must be viewed from the side as seen here, in the deeper color of the polarized o-ray. The resultant spectrum shows the usual broadening of the central band to eliminate all green and a strengthening of the fluorescing doublet in the deep red. The lines in the blue remain vague and violet is absorbed.

Corundum Spectra
CORUNDUM DOUBLET (ε ray)

Color due to chromium. The green sapphire crown on this doublet is too thin to be detected in the spectrum. The result is a typical chromium spectrum from the lab created ruby pavilion with the fluorescence lines in the deep red and absorption lines in the blue. The absorption band in the green is of moderate width. As in all chromium spectra the violet area is totally absorbed. On rotation of the polarizing filter to isolate the e ray, the central absorption band has now narrowed to allow more transmission of the orange and green. Other lines have also lost intensity and are less sharp.

Jewelry Television acknowledges the significant scientific contributions of John S Harris, FGA to the study of gemstone spectra and with deep appreciation to him, acknowledges the use of his images and related notes about gemstones and their spectra in the educational materials on this website.

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Tim Matthews

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Tim Matthews

Tim Matthews is President and Chief Executive Officer of Jewelry Television® (JTV), as well as a member of the company's Board of Directors. He oversees and leads all aspects of the company's powerful omni-digital retail platform that uniquely specializes in fine jewelry and gemstones. His passion for business and gemstones has led him to become a recognized expert in the field of gemology. He is a life member of the Gemmological Association of Great Britain (Gem-A) and has earned Gem-A's highest degrees, the Gemmology (FGA) and Diamond (DGA) diplomas. He is also a Graduate Gemologist (GG) of the Gemological Institute of America (GIA) and has also completed GIA's Graduate Diplomas in Diamonds, Colored Stones and Pearls. Under his leadership, JTV has become the leader in the sourcing and selling of color gemstones and jewelry.

This page was created on June 27, 2014.

This page was last edited on October 24, 2019.