Travel Stories

Natural Corundum || Sri Lanka - Land of White Smiles and Cornflower Blue Sapphires

Travel Stories >> Natural Corundum

Much of what I have learned about precious stones comes from an Italian book called, "Il Tutto: Pietre Preziose". And much of what you will read here has been gleaned over time from that text. I have always been fascinated by colored gemstones, and until I went to Sri Lanka, I had no idea how many different precious and semi-precious stones come from there. Before studying my Italian's book, I had no idea that the Italians were such experts on stones. Once I had my Sri Lankan stones set by a jeweler in Italy (Florence, specifically), it all began to make more sense!

There is no doubt that precious (and even semi-precious) stones have been prized for centuries in a variety of forms, and for a variety of reasons. In ancient times some stones were thought to bring magical powers to the owners, others were thought to ward off evil. Some stones were carried by their owners for medical reasons, or to prevent certain diseases. For centuries royalty and the church had gems and precious metals, the poor did not. Even today it is the wealthy who can afford the big, expensive jewels while the rest of us are more likely to admire, appreciate, and own semi-precious stones. And even today most of us know our "birthstones"; those gems which are arbitrarily assigned to either zodiac signs, or months of the year.

Although a large gemstone can be impressive, what makes it precious is not its size. The following factors are what makes a stone "precious": rarity, hardness, the fact that it is in its natural state, and its beauty. Of course, rarity and beauty are subjective... and there are plenty of synthetically produced gemstones found these days that are not rare because they are man-made and do not occur naturally. But hardness is a factor which is not disputed. Gemologists are scientists, and their science is one of chemistry, physics, and geology. Gemstones are classified by their crystal properties, their symmetry, their chemical make-up, their optical properties (refractiveness), their density, their cleavage (yup! means their brittleness or ability to break), and other factors.

Most people know that diamonds are the "hardest" stones, at a grade of ten (10). A gemstone's hardness is a result of the "cohesion of minerals" that make up that stone. The book says, "[hardness] is definable in terms of resistance to external stresses: scratching, abrasion, penetration. The scale of gemstone hardness is called Mohs' scale and all stones fall into this scale - from hardest to softest:

	10	Diamond
	9	Corundum
	8	Topaz
	7	Quartz
	6	Orthoclase
	5	Apatite
	4	Fluorite
	3	Calcite
	2	Gypsum
	1	Talc

Perhaps you read this and think, "yeah, but where are emeralds and amethysts, or rubies.". Your favorite stones are classified within one of these classes or another (except the diamonds, of course). Rubies and Sapphires are classified as corundum and next to diamonds they are the hardest stones.

But there must be more to a stone's value than its hardness. While Roger and I were in Sri Lanka we were taught a lot about what to look for in a good stone - and how to recognize the value in a gemstone. We were told a number of things: The "color" of a stone is the first sign of value. The color of a stone depends on the extent to which it absorbs light rays. The color of a good stone should be solid and uniform, the same when viewed from every angle of the stone. What also makes a gemstone attractive is its "luster". Like with hardness, gems can be identified by their luster as well. The harder the stone is, the greater luster it will have. The luster of diamonds is classified as adamantine, rubies and sapphire as vitreous, turquoise as waxy, moonstones as pearly, gypsum as silky, and hematite as metallic.

The "cut" of the stone is the second sign of value. A beautiful stone can be cut poorly, and if so, will not reflect the highest luster and color that it might otherwise. The sapphire we bought for Roger's ring was a beautiful stone, however when Roger questioned the cut, our friend Weera suggested we might gain by having the stone recut. Once recut (the stone lost only .03 ct weight) the value of the stone increased enormously.

Back to "Natural Corundum", our topic at hand. Corundum is Aluminium Oxide. My book tells me that the name probably comes from the Indian word corund which means 'unknown stone or mineral'. Although often opaque or translucent, it can appear completely transparent as well. It comes in all the colors of the spectrum (sapphires can be found white, green, yellow, pink, and all sorts of blues) although the two best known varieties of corundum are the red ruby and the dark blue sapphire. As we have read, corundum has a hardness of "9". For the geologists (Mr. Powicki?) amongst you, I'll include here that corundum is formed by, "contact metamorphism between alumina-rich magmas and limestone, or by regional metamorphism of alumina-rich, silica-poor rocks." Sounds easy doesn't it? Like we should all be able to wade through any stream and just scoop up the rubies.

The gem varieties of corundum are found in Sri Lanka, Thailand, Cambodia, Burma, and Australia. Less significant deposits have been reported in countries like the US, India, and Tanzania as well.

*RUBY (Al2O3)*
	The most valuable of the natural corundum is the ruby (from the Latin rubrum or, 'red'). the color of a rubies varies greatly from a deep vermilion to a very violet red. A number of people have gazed upon my ruby ring and asked, "is it a ruby or a pink sapphire?" And the following text gives the answer (they are the same, basically!):
		"The color of a ruby varies from fiery vermilion to violet red, but because rubies are pleochroic, different colors can be found in the same stone. The color is also accompanied by a marked 'fluorescence' which is stimulated by ordinary, artificial light, and also by the ultraviolet rays of direct sunlight. Some red rubies will turn brighter red under such light and purplish rubies look redder. If the color is very pale they may be called pink sapphires, the more violet called violet sapphires. but it is hard to establish precise limits as all the intermediate shades are possible. [T]he most valuable rubies often have areas of inclusions in the form of minute 'rutile' needles (or straws), which interfere with the light, producing a silky sheen, known in fact, as 'silk'."
	Although tests for hardness, and the refractive index of a ruby can be done by a trustworthy jeweler, one of the simplest ways to tell the difference between rubies and the many other reddish gemstones such as the red spinel, garnet, and the red tourmaline is that the ruby will always brighten and become more lusterful in strong light. In addition to the silk effect, when it is present, this heightening of luster is a result of the ruby's 'pleochroism' and is not evident with other red stones. Although my trusty book tells me a lot about the differences in the rubies from Burma and Thailand, they say that the rubies from Sri Lanka tend to be a more violet/pink red and are well known for an appearance which is, "brilliant and lively".
	One might note here that one of the other things we learned in Sri Lanka, about the gems we were seeing, is that it is normal, expected, and sometimes value added to find inclusions called silks or feathers or needles in the stones. We realized how clean and beautiful our own stones were with their hardly-visible-inclusions while we were in Italy. We were disappointed to see most of the rubies and sapphires in ring and pendant settings in Florence were badly marked with inclusions. Although this is a sign that the stone is not synthetic, nor even a good imitation, it is not as pleasing to look at. It is true that a good setting can help to hide a small flaw or inclusion, but if the stone is muddy with inclusions, leave it for the next guy.
	Finally, the ruby has been produced synthetically (primarily for industrial use) from early in this century and was in fact, the first gemstone to be manufactured on an industrial scale.
*SAPPHIRES*
	The sapphire is the blue variety of the corundum... Although the word sapphirus in Latin, and sapherios in Greek may have come from a Sanskrit word and mean blue stone, it is now believed these words referred to what we know today as lapis lazuli rather than our sapphires.
	Sapphires can range in color from very dark blue (and can be seen as almost dense and blackish) to a pale blue. Although it is called the blue stone, sapphires are also found in Sri Lanka, in particular, in tones of violet or canary yellow. Many of the sapphires we saw set in rings in Sri Lanka were surrounded by white stones; not diamonds but white sapphires. We were told that the color of the sapphire depended a great deal on the degree of heat it was exposed to while being formed.
	Although it is hard to see inclusions (called 'veils' or 'feathers') in the stones of very dark blue, they are commonly seen in the lighter stones. Like other types of corundum, the sapphire is a hard gem ("9") and is known for its striking luster. The sapphire has a greater tendency to be found with less even color than other corundum. The color of a sapphire can tell a gemologist where that stone is from,
		"..a deep blue color with distinct blue-green pleochroism and internal streaks straight across... indicates a sapphire of Australian origin. A slightly patchy, blue with imperceptible pleochroism and strong transparency showing veillike inclusions and a slight silk effect still with excellent luster, denotes a sapphire from Sri Lanka. Cornflower to deep blue in a stone without obvious inclusions but of a slightly milky appearance is characteristic of the rare sapphires of Kashmir"
	Distinguishing sapphires from other blue stones like the tanzanite, or cordierite tends to bring us to the same benchmarks we find with the rubies; the deep luster and the brightening of the stone in strong light. Tanzanites tend to be more purple (and are considerably softer), and Cordierites usually hint of grey or yellow behind their blues.
	Our book tells us that a significant quantity of light and bright blue sapphires are found in alluvial deposits on the island of Sri Lanka. They state that the color is very attractive and is similar to the rarer Kashmir sapphires and equally as valuable. They also note that:
		"The sapphires of Sri Lanka are also famous for the variety of inclusions they display: long, thin rutile needles, like very fine silk; soft liquid inclusions arranged in the form of veils, lace and feathers; striking inclusions with a moving bubble, like a spirit level.."
	The finest sapphires are found in Burma, Kashmir, Sri Lanka and some from Thailand and this book lists them as almost as valuable as diamonds and rubies. They note that if a sapphire is too dark, too green, or too pale, its value will drop sharply.

(top)