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We have selected samples from C.I.G. 's comprehensive gem study collection which are difficult to identify. Most pictures were taken with an immersion-scope (methylene iodide); under a common "dry" microscope with dark-field illumination many features shown here may not be visible. A detailed booklet with computer diskette containing over 100 micro-photographs is available from Gemlab Book Services . © 1996 J. W. Kuehn

Description of inclusion features have been provided by Peter G. Read

508Linde synthetic Star Ruby

510Knischka synthetic Ruby

Developed by Prof. P.O. Knischka, this synthetic ruby is recognizable in the rough crystal by its spindleshaped, multi-facetted shape. Facetted stones (these aren't yet widely distributed) may contain phantom-like clouds of dust particles (similar to those seen in Burma rubies).

Other more diagnostic internal features include swirls of colour; irregularly shaped, net-like liquid feathers; parallel negative crystals having- the same bipyramidal habit as the host crystal and appearing at the end of long crystal tubes; black, distorted hexagonal platelets of platinum and silver; and two-phase inclusions (with ill-defined void boundaries and conspicuous bubbles), this last feature being regarded as an identifying characteristic of Knischka rubies.

When visible on a spectroscope, an absorption band between 250 and 400 nm is a clear indication that the ruby is a synthetic (this band is more easily detectable on a spectrophotometer). The Knischka rubies that have been inspected so far show little iron content, and therefore have a high S.W. U-V transmission factor.

511aLechleitner synthetic Ruby

511bLechleitner synthetic Ruby

513Ruby, natural

514Ruby, natural, Africa

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