Zircon

Color due to heat treatment. The diagnostic absorption line at 653nm; and a weaker one at 662nm; both lines being rather diffuse.

Color due to uranium and radiation damage. Although dichroism in this zircon is unusually strong, changing from a pronounced brown in the o-ray to a dark green in the e-ray, the spectrum changes very little apart from the width of the dominant strong band in the red centered at 655nm. This indicates it is possibly an intermediate type without a fully crystalline structure.

Color due to uranium and radiation damage.This large dark orange brown zircon of 11cts. from Sri - Lanka displays most of the absorption lines associated with fully crystalline high type material. However the dark orange brown color absorbs strongly in the violet - blue areas making resolution of the lines there difficult. The diagnostic lines at 653nm. and 661nm. are seen at their strongest when a polarizing filter is used to locate the ordinary ray.

Color due to uranium. This light brown Sri-Lankan zircon shows very little apart from the dominant line in the red at 653nm. and the faint 661nm. alongside

Here we see the lines at 653nm. and 661nm. become two lines of equal width and intensity with other lines also appearing. A very faint indication of the two lines at 615nm. and 621nm. can just be seen

Color due to uranium and structure changes. A weak and difficult to see fuzzy band from 650nm. to 662nm. and indistinct images of other lines suggests this could be an intermediate type zircon

Color due to uranium. The typical lines at 653nm. and 660/662nm. are less distinct

Color due to uranium. The original color of this zircon from Myanmar was a bright greenish yellow. After heat treatment to about 900'C in an attempt to produce a deep violet blue color the aborted experiment produced this almost colorless stone which is not unlike a cape series diamond of low color grade. However, the strong sharp spectrum associated with zircons from this source remained intact as seen here.

Color due to uranium. The spectroscope here reveals the diagnostic line at 653nm. which, seen here in the o ray, is strong and about 4nm. wide. This is accompanied by the two faint and narrow lines on the long wave side at 660/662nm.These last two lines are usually only resolved by a small hand spectroscope as a single line at 661nm. Other faint lines are seen in the blue and green

Color due to uranium and structural changes. A weak fuzzy band from 650nm. to 662nm. and indistinct images of other lines suggests this could be an intermediate type zircon

Color due to uranium. Red zircons generally do not show a strong pattern of absorption lines compared to some other colors of zircon. The o-ray chosen here shows the dominant line at 653nm. at its strongest, but the normally strong line at 589nm. is but a weak smudge. Only vague images of the two lines at 484nm and 460 can be seen in the blue. Some red zircons do not display any lines at all

Color due to uranium. A line at 653nm. becomes sharper and stronger as an indication of the o-ray together with the weaker lines alongside at 660/662nm. Various other fine lines appear throughout the spectrum but are too weak and narrow to be captured in this image

Color due to uranium. Dark red zircons like many red stones often have a brownish overtone and do not transmit well in the deep blue-violet area of the spectrum. In some, unlike most zircons, there are no obvious lines to be seen not even the usual diagnostic line at 653nm. On close inspection only a few vague shadows can be detected about 590nm 520 nm. and 500nm. close to where some prominent lines may be seen in most other colors of zircon

Color due to uranium. As the e ray is polarized, although the stone appears the same, the spectrum changes in that the lines at 615nm. And 621nm. are present and stronger.

Color due to uranium. However, the indication of the o ray is seen in the spectrum by the absence of the two lines at 615nm. and 621nm. in the orange. Note in the unpolarized spectrum above these two lines are just visible but are very faint. Slight variations also occur in the strength of various other lines.