Birthstone Spotlight: September Sapphire

sapphires

Sapphire is a lot bigger subject than might be thought by the casual observer. For many years, many people thought sapphire was simply that very dark blue stone in small sizes offered by most jewelry stores as the September birthstone. Sapphire is certainly that, but ever so much more…

How Sapphire and Ruby are related

It is no wonder that we associate the color blue with the word “sapphire” since the origin of the word is from the Greek “Sappherios,” which translates as “blue stone.” As science started categorizing gems and the minerals of which gemstones are comprised, it was decided that the gems we now label as sapphire would be known as the mineral corundum.

Corundum is crystalline aluminum oxide, and encompasses both ruby and sapphire. “Aluminum” may sound rather humdrum on the one hand—as in foil, airplane parts and automobile engines—but it’s no different than calling diamond “carbon,” as in charcoal briquettes, coal, and carbon footprint. There seems to be a lesson in this regarding humble beginnings…

Sapphire colors

Once it was decided by the science community that sapphire would be the blue gem made from corundum, it turned out there are a whole lot of other colors of corundum / other gems made from corundum that were other colors. Oops!

Red corundum is ruby—as long as it is colored by chromium. But all other colors of corundum are now considered to be sapphire. And, what a wonderful thing that is.

sapphire mine madagascarSapphire mine in Madagascar

Blue Sapphire, and where it comes from

You will never know how many colors of blue exist in the world until you start seriously shopping for blue sapphire.

For many years the majority of sapphire sold in jewelry stores was overly-dark sapphire from Australia. These stones were not only too dark but they normally had a secondary green component. The main advantage of these gems was that they were inexpensive (at wholesale) and plentiful. However the issue true gem lovers had with these stones was their truly inferior color. In the case of blue sapphire the color you want is blue with overtones of blue (i.e., no overtones).

Sapphire Queen Silvia SwedenSome truly fine colors of blue sapphire, including many large and famous sapphires came from Sri Lanka (also known as Ceylon). There are Ceylon sapphires in the collections of the Russian Crown Jewels, the British Crown Jewels, the Smithsonian Institution, and the American Museum of Natural History in New York. These gems generally have a very pleasing color that is well saturated but not too dark. These museum stones also tend to be in relatively large sizes.

There are a couple of other sources of sapphire in Asia which are reputed to have even better color than the gems from Sri Lanka, namely Myanmar (Burma) and Kashmir. From the examples I have seen, the sapphires from these regions are very similar in their blue color, but  even better than the Ceylon stones. Generally the issue is saturation of color: this is where the Ceylon stones fall down in comparison to Burmese and Kashmiri stones. The Ceylon stones have just the slightest impurities in their color. The difference is so subtle that it is really perceptible only by comparison.

In the past decade there have come some sapphire gems from Madagascar which are incredibly beautiful. Having to choose between the best of all these gems is a little like having to choose between the best European supercars—Lamborghini, Ferrari, McLaren, and so forth. What’s not to like in all of them. The true collector says “I’ll take one of each!”

Montana Sapphire Missouri RiverOne unexpected locality of origin for sapphires is in North America, along the Missouri river near Helena, Montana. Years ago I bought big quantities of this material from a miner. The deposit there is alluvial. Alluvial deposits of sapphire have been eroded away from their original place of formation and re-deposited (his is true of any alluvial material, from road gravel to gold nuggets). One thing that sapphire has in common with gold is a specific gravity greater than many other minerals. Of course gold is heavier than sapphire (aluminum vs. gold), however since both are heavier than average rock, both gold and sapphire can be found together.

As minerals have been eroded away from their place of origin they become deposited according to their specific gravity or specific weight. Items with a higher specific gravity or heavier specific weight slow down first and tend to group in a bend of a stream or river together and before materials with a lower specific gravity or specific weight. So, in the El Dorado Bar outside of Helena, Montana gold and sapphire can be found in the same ground!

Yogo Gulch Montana SapphiresSapphires found in Yogo Gulch, Montana

How they got there is really fascinating. According to scientists during one of the last Ice Ages there was a giant lake being held back by a glacier. As the warming of the climate occurred at the end of the Ice Age the glacier damming the lake gave way in cataclysmic way that created a scouring of the earth like nothing we have seen in recorded history. Apparently the host rock of the sapphire and gold were in the path of the water, were carried along for a distance and were deposited together once the speed of the water slowed sufficiently. What a sight that must have been!

There are two other significant deposits of sapphire in Montana (people may well say there are more). The other two are Rock Creek near Phillipsburg and Yogo Gulch in the Little Belt Mountains in Judith Basin County. Rock Creek has produced perhaps tons of sapphire over the last 6 decades. The stones from Rock Creek tend to be small but relatively clear of inclusions. The Yogo Gulch stones tend to be clean and to be of a naturally fabulous color. Since as many as 90% of cut sapphires in the world are color enhanced after mining, the Yogo stones are notable for coming out of the ground beautiful and ready to cut as-is.

star-sapphireStar Sapphire

A little known and little remembered type of sapphire is known as star sapphire. Star stones get their name from a phenomenon known as asterism. Star sapphires exhibit what looks like a six-rayed star when a single source of light shines on them. Star stones are judged in quality by how sharply and well defined the star is exhibited, by the color of the stone, and by the clarity and translucency of the piece.

The star itself is created by the play of light over inclusions oriented along crystal axes. Corundum forms in hexagonal crystals. A “hexagon” is a six sided polygon. Hence the six rayed star. Star sapphires are cut en-cabochon (round and smooth as shown above).

There once were more star sapphires for sale than currently but it was found out that heat treating a star sapphire would increase its color while getting rid of the star. This also increased the dollars per-carat of the finished piece. So, many stones that could have been cut into star stones were heat treated to improve their color, only to get rid of the star and to reduce the number of star sapphires on the market.

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One thought on “Birthstone Spotlight: September Sapphire

  1. Pingback: Scintillating Sapphire by Laura Ramsey | John and Laura Ramsey • Gems at Large • Ramsey Gems

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