The Pleasures Of Discovery

(via The Journal of Gemmology, Vol.XIV, No.3, July 1974) B W Anderson writes:

(being the substance of a talk given to the Gemmological Association of Great Britain at Goldsmith’s Hall on 29th October, 1973)

Kornerupine
One thing leads to another. During our search for blue spinels of high refractive index in parcels of mixed Ceylon stones, we had come across a few specimens which we couldn’t identify. These were brownish green in color, had a density nearly matching that of methylene iodide (3.33) and refractive indices 1.670 – 1.683. They were strongly pleochroic from pale brown to dark green and had vague absorption bands in the blue and violet. We put them on one side in a packet, labeled ‘Y’, as we could find nothing in the tables of mineral properties to tally with these constants.

At that time I was very interested in the absorption spectrum of enstatite, since we had found that the attractive green pebbles from Kimberley showed a beautifully clear cut line 5600 Angstrom and I wanted to know whether specimens from other localities showed the same. The Natural History Museum had in their collection a cut stone weighing 9.18 carats, which had been rescued from an ‘idocrase’ box by Dr Herbert Smith on the basis of a refractometer test, and more plausibly labeled ‘enstatite’. I asked permission from then Keeper of Minerals, Dr L J Spencer, to examine the stone, and we found that it was not enstatite, but did tally closely in properties with our unknown ‘Y’ specimens. Naturally the Museum people were now interested, and Dr Claringbull by X-ray analysis was able to identify our unknowns as kornerupines of a hitherto unrecorded type. Previously the only gem quality kornerupines known were pale aquamarine-colored stones from Madagascar, containing less iron and with rather lower constants.

By one of those lucky and highly improbable chances with which we have been favored from time to time in our work, a mounted kornerupine of ‘our’ kind was sent to us for testing by a York jeweler. I was able to purchase the stone (which weighed 6.74 carats) for a reasonable price: the jeweler was very happy to replace it by a tourmaline rather than to try and sell a stone which had a name quite unknown to the public. A slice was removed from this for analysis, the recut stone weighing 3.50 carats.

Kornerupine is a complex borosilicate of aluminum, magnesium and iron, and the chemical analysis, undertaken by Dr Max Hey, was unusually difficult on a micro-scale, owning to the presence of boron, which several previous analysts had missed. For Dr Hey, this developed into a major piece of chemical research into the best methods for analysis of this difficult subject and a re-assessment of all previous analyses.

Meanwhile our main concern was to prove that these ‘new style’ kornerupines did in fact come from Ceylon, which we strongly suspected from the company they kept, by the style of cutting, and some of the inclusions. Through the kindness of Mr Hans Van Starrex we were sent two generous consignments of the gem gravel from Matale, and from the first of these, after about an hour’s search, we were delighted to find the first recorded kornerupine from the illam of Ceylon. Twenty minutes later another turned up—but in the second parcel there were none. My method was to segregate the pebbles of likely color, then quickly run through them with the spectroscope, eliminating all the zircons, which formed the bulk of the parcel. Any stones which seemed possibly to be kornerupine were passed to Mr Payne who examined them with a dichroscope and checked their density in methylene iodide, in which kornerupine remained virtually suspended.

The long chemical investigation naturally involved delay, and it was not until more than two years after the war had started that the full details were published. After the war, Mr Kenneth Parkinson, on one of his several successful visits to Ceylon in search of rare gemstones, returned with a cut kornerupine weighing 9.89 carats and a large piece of rough weighing 24.12 carats. This was unusual in showing traces of prism faces and is now in the collection of the Natural History Museum. And at about this time Dr E H Rutland sorted through some 15 lb. of illam provided by Mr Reggie Mathews, and was able to recover 8 kornerupines, which yielded cut stones ranging in size from 0.30 to 1.15 carats. These were mostly the usual brownish green, but some were distinctly green and one was yellow.

Before leaving kornerupine, let me say just a word about another ‘new’ occurrence of the mineral which we were the first to establish.

About 1937 we had acquired a small but very pretty green stone weighing 0.22 carat, which had refractive indices and density near those of the Ceylon kornerupines discussed above. After these had been identified by the Museum we realized that this stone, too, must be a kornerupine, but from some other source. Not until August 1952 did we know that this source must be the Mogok stone tract in Burma, for it was then that A C D Pain submitted for test a collection of interesting stones, all from Burma, amongst which was a bright green specimen with only the table facet polished, which we identified as kornerupine. The color, the inclusions and the properties were close enough to ours to make us sure that the origin was the same. It is curious how the jingle ‘anything you can do, I can do better’ seems to be appropriate when it comes to Burma versus the Ceylon gem fields.

The Pleasure Of Discovery (continued)