Introduction:

Original imagery as taken by AJS Gems.

This is part 1 of 3 in a series of a study of corundum specimens. This document entails a study using micrographs and various non-destructive study and examination with instrumentation available. This document details observations as noted, along with supporting imagery.

The first specimen examined was a purple sapphire disclosed as being heat treated in a manner that virtually all sapphires are treated in (with some rare exceptions). The specimen was also disclosed as originating from Madagascar.

Objectives:

The following objectives were defined in this study.

1. Is the stone examined in fact natural or synthetic?
2. Is there any evidence of additional of different thermal enhancements other than those disclosed at the time of sale?
3. Is there any evidence to support the origin of this stone?

Background:

There is very little information that is conclusive as to purple sapphires that are published and readily available. What information that is available online collectively is conflicting or inconclusive as to properties of synthetics with respect to UV fluorescence, chemical composition, etc.

As with any synthetic corundum, strong fluorescence of certain colors denotes a synthetic. This particular specimen appears to glow pink to pinkish red under exposure to UV-A using a hand held UV lamp. Many sources cite this as being a tell tale sign of a synthetic. However, the GIA published an article in Gems and Gemology citing a moderate to strong fluorescence in purple sapphires from Pakistan. The material used in the study was said to be in the range of light purple to shades overlapping amethyst and plum colors. It also cites origins of like material to be from Tanzania, Ceylon, etc.

Based on that source, the test for UV fluorescence is inconclusive as to the stone being natural or synthetic, and it doesn’t conclude the origin to be Madagascar or anywhere else. So as such, we have another possibility of origin.

Much is published citing vanadium as being the coloring agent for purple sapphire, and other sources suggest this to be what is responsible for making some sapphires change colors. Other sources suggest the purple being the mixture of a sapphire and a ruby. In such a case, titanium with chromium would blend in the aluminum oxide matrix, and accept iron as a toning agent to produce a certain color. In either case, it would be a rare combination of elements to combine as such to produce this material. Regardless, many sources say that where rubies and sapphires are found, purple sapphires are found as well. This would imply (at least) that is possible for this stone to be from Madagascar since it is a known source for both rubies and sapphires.

With regards to origin, renowned expert Richard Hughes illustrates in published material certain corundum’s from Madagascar appear to be the exception to the rule with regards to fluorescence under UV exposure and various treatments being present or absent. However, there is nothing noted (online) about purple sapphires in general.

Methodologies:

A portable microscope was used with an LED light source built in. The microscope is digital, and it is capable of rendering imagery on a laptop without the use of compression. This can reduce if not exclude the presence of various artifacts that compression algorithms induce.

A household kitchen light source was used to work with, and a hand held UV lamp was used to test for long wave radiation. Additionally, a laboratory arm with tweezers was used to hold the specimen in place for the study.

General Characteristics of Specimen:

The specimen in question is believed to be a purple sapphire as was represented from the sale from this vendor. The stone has a carat weight of 2.91 carats. It is cut as a modified emerald cut in the shape of an octagon. It measures 8.60mm x 5.50mm x 5.70 mm based on vendor documentation.

Under various lighting conditions, purple is the dominant color. Diffused lighting through a cotton background in direct sunlight makes the stone appear bluish purple as well as under mercury vapor lamps. Under some incandescent lighting, it appears more pinkish purple, and under strong halogen lighting, it also appears to be more pinkish purple. The stone faces up eye clean with maybe the exception of what is suspected to be some wax from the doper that doesn’t clean up very readily.

Fig 1. This is a view of the stone from somewhere between 10 and 15 magnifications. This is the view with line of sight being the c-axis or thereabouts. The orientation is such that the table is facing upwards towards the microscope.

Previous experiments had shown eye visible fluorescence in a darkroom environment with exposure to UV radiation. The closer the source of UV was placed near the stone, the more intense the emission of visible light as a result. Under the same conditions with protective UV filtering eye wear, the glow is quite red though softer. This suggests the presence of chromium within the crystal matrix.

Additionally, there was some noticeable color zoning of an inert purple in triangular patches near the edges of the stone. The zoning looked somewhat like zoning seen in some synthetic materials under oil immersion, but this observation was not done with oil immersion testing.

Under the loupe, there is some visible zoning, though it is hard to tell how curvilinear the growth rings appear to be due to the orientation of them, the faceting, and visibility through the axial ends of the stone. So as such, there was nothing conclusive either way about anything. There was a veil of rain on the side of the stone, however it appeared as if there were 2 planes being angled with respect to the other. This is not consistent with the liquid phase inclusions in synthetic stones, nor was the presence and consistency of a circular pattern observed. That would support the fact that the stone is natural, and the color zoning also seems to support that.

Micrographs and Observations:

With a standard light source that is generally accepted for grading or equal source, the stone is eye clean other than possibly some lint or dirt. As illustrated in Fig 1., this stone has a dichroic appearance under the LED lights of the scope and with ambient lighting in the room in which the study was conduced in.

There is a strong blue fluorescence that is viewable from the middle through the pavilion, and some like behavior near the girdle. This same effect is noted from the axial ends of the stone when rotated 90 degrees about the table plane. This blue fluorescence rivals that of some Burma sapphires I’ve seen in person. It is difficult to capture this as accurately with the equipment available. These are things that are not seen with synthetic stones. However, by and in itself, I wouldn’t say it’s conclusive.

The magnification was increased to an estimated 30x-35x. The view and orientation was kept the same as the stone was suspended above a neutral colored surface with the use of spring action tweezers mounted in a mechanical arm.

Fig 2. This is between 30 and 35 magnifications. If you look through the crown on the left axial end, straight line growth rings can be seen orthogonally with respect to the east-west axis as oriented. There is some color zoning noted also.

Fig 3. This is the same view without ambient lighting present, and only the LED’s from the microscope itself. We can see a stronger pink fluorescence and the color zoning is more obvious here.

Since we had a lack of ambient light, an the dominant source of light was from the microscope, an attempt was made to observe the behavior of the stone under UV lighting while under the same magnification.

Fig 4. Under near darkroom conditions, a UV lamp is placed beneath the stone in close proximity to the stone. We can see some variation in the color, and we can see something appearing to be more orange in color, and more definition in the color zoning.

Fig. 5. Within a few seconds of the lamp being removed, we can observe a fluorescence emitting from the stone, and yet another view of the growth rings and color zoning as in the above figure(s).

After observing and photographing the stone under the conditions as described with each illustration, the stone was wiped with an alcohol pad to remove some lint that had found its way there to rule out certain inclusions.

Fig 6. This is how the stone appears with ambient light and the LED light source of the microscope under ~40x.

Fig 7. This is how the stone appears with ambient light and the LED light source of the microscope under ~50x.

Fig 8. This is how the stone appears with only the LED light source of the microscope under ~50x.

Under microscopic examination, with the absence of ambient lighting to interfere with the imagery obtained, we can see the zoning and growth rings more readily. There is a distinct lack of curvilinear growth. We can see some evidence of other artifacts that appear to be discoid fractures and other solid phase inclusions.

Fig 9. This is the stone in the presence of a UV lamp as above at ~50x.

Fig 10. This is the stone with UV lamp removed. This image is after a few seconds after the UV source was removed (~50x).

Normal working conditions were restored, and magnification increased to ~60x.

Fig 11. At ~60x, we can see some distorted solid phase crystals that have melted due to thermal exposure. These are shown in the upper right corner of this image.

At this level of magnification, we can see the presence of discoid inclusions in various places of the stone more readily than in other imagery. We can also begin to see certain single phase solid inclusions that do not readily adhere to any typical crystalline shape. This is common in any thermal enhancement.

Fig 12. The center of the image illustrates the presence of a discoid inclusion near the lower right corner of the stone as shown. Near the upper left corner of the image, we can see part of what appears to be a fingerprint inclusion near another discoid inclusion. We can also see some melted crystals with terminal ends, though distorted in parallel to each other. Within the vicinity of those same inclusions, we see what resembles a series of comet tail like inclusions.

Fig 13. We can see the discoid inclusion from the previous image in addition to a second inclusion of like kind. We can also see evidence of distorted crystals near the center of the discoid near the center top of this image. The top most crystal takes a generic form of a single axial ended sapphire crystal though it is misshapen in appearance. We can also see some evidence of a healed fracture.

Fig 14. The inclusion near the top center of the image illustrates another discoid in addition to what appears to be a healed fracture. We can see what looks like a series of comet tail inclusions from a healed fracture, and various small and misshapen crystals. It appears as if this discoid is a multiphase inclusion.

Fig 15. We can see some of the color zoning and growth rings in greater detail between 60 and 62 magnifications. There was some delineation observed, but this was very minimal. It is clear that the growth lines are very well in tact with only the most subtle of variations. There is also evidence of a lack of uniformity in the intensity of color and width of these zones.

It was deemed a point of interest to try and get a closer look at various inclusions, and thus the magnification was increased to ~110x.

Fig 16-17. These are 2 orientations of the same stone. The magnification was increased to 110x. The inclusions shown are what appears to be part of a rain veil or other small solid phase inclusions. These do not appear to be in any pattern consistent with synthetics, and appear more like a rain veil under a different orientation under a loupe.

From this point, the stone was repositioned to view the axial end to examine it more closely. Viewing it under the loupe was rather confusing, so it was of interest to view it more closely under the microscope.

Fig 18. There are 2 discoids near the facets beneath the girdle of the stone. We can also see other inclusions scattered throughout the stone. We can observe growth rings in 2 directions if we look towards the other axial end through the crown. There is some evidence of polish marks seen near the girdle, though not as prominent here at ~35x-37x.

Fig 19. This is the same image in the absence of ambient light from the room. The polish marks are more readily observed.

Fig 20. This is the same view as above without ambient room light. The magnification was increased here to ~47x.

Fig 21. This is a repositioned view of the same stone under the same magnification. This was done to further examine what appeared to be an orangy color zone as showed.

Under magnification, we can see evidence of discoids and a very unusual color zoning of orange. We can see other artifacts that appear to be slightly out of focus from the view of the axial end of the stone looking through the pavilion. We can observe shades of purple, orange, pink, and blue hues.

Conclusions:

1. The stone does not appear to be a synthetic due to the lack of red fluorescence under microscopic examination.
2. The absence of curved striae and the absence of monochromatic zoning do not support evidence of a synthetic stone. The growth lines are straight with minimal deviation. This miniscule deviation is consistent with high temperature heat treatment (HTHT) with sapphires.
3. The presence of discoids indicate that there were 2 phase inclusions from tension fractures that expanded during the HTHT process. This is a tell tale indicator.
4. The presence of solid inclusions denotes that they are deformed, thus supporting HTHT as disclosed.
5. The presence of healed fractures and the (partial) finger print inclusion are consistent with HTHT inclusions.
6. The presence of comet tail like inclusions is an indicator of Madagascar origin.
7. The zoning suggests trace elements present in a composition that to date is exclusively Madagascar in origin.

While figure 21 shows what looks like a color core, there is a lack of evidence of beryllium treatment that can make sapphires appear orange through lattice diffusion heat treatments or bulk diffusion treatments. We can observe and conclude the following:

1. The stone is purple, and not orange. The anomaly illustrated is visible only under microscopic examination, and there is not a consistent color core throughout the entire stone as one would expect in a diffusion treated stone.
2. There is an absence of consistent color zoning around the girdle; this is a tell take indicator of a diffusion treated stone. There is not any zoning attributable to repolishing after diffusion treatment of any kind.
3. Diffusion treated stones tend to exhibit a very monochromatic glow. Growth rings only differ by subtle shade variations of the same color under such treatments. We can readily see that we have distinct color changes and not just subtle shades from one zone to the next.
4. Beryllium treated stones exhibit a very distinct halo pattern throughout the stone-particularly near discoids. Fingerprint inclusions would also have these same halos around them, and be more abundant.
5. Color zones in diffusion treated stones tend to be thicker, more uniform and consistent. Natural color zones are not so readily consistent.

It is worth noting that Richard Hughes illustrates an unusual orange color zone in an unheated sapphire that will fluoresce orange in a patchy area in a like manner as the illustration in figure 21. He says that this is an anomaly that is found exclusively in Madagascar sapphires.

While no claim is being made to say that this stone is unheated, the findings of Hughes seem to suggest that these unusual zones that are natural could be a tell tale sign of origin. There is research being done according to GRS (and/or Hughes) that says these anomalies are attributable to the presence of elements as boron and lithium in trace amounts. They seem to alter the behavior of corundum’s exposed to UV sources.

While there are some patches of green that are observed in the images, it is unclear as to if this is an artifact induced from the camera, or if this suggests the presence of vanadium as a trace element. It is a known fact that amongst other metals, vanadium can be responsible for pleochroism in many stones. Some sources say that in very rare cases, color change sapphires can change from pinkish purple or pink to green. Typically, these things change from purple to blue.

There is evidence to suggest the presence of various trace elements (including vanadium) in the stone as well as other things. However, further testing would be required to quantify the particulars. The same tests would also likely confirm the origin and such. Based on imagery from GRS and another laboratory from Asia, the inclusions and unusual color zoning support Madagascar as the likely origin of this stone.

-joe