Tag Archives: traditional birthstone

September Shades

I realized that I haven’t geeked out over the gemology of birthstones in a while. So a slightly late visit to September’s traditional birthstone, sapphire.

Sapphires are a gemstone variant of corundum. Red gemstone corundums are known as rubies, every other color is categorized as sapphire. (Despite the very name coming from a Greek word for blue.)

For a long time the word sapphire was applied to different stones. Even into the Middle Ages a reference to sapphire was probably to what we now call lapis lazuli.

Corundums are composed of an aluminum oxide, the bond between the aluminum and the oxygen atoms are short and the atoms are nestled tightly together. This makes them comparatively dense despite being made of light elements, and it makes them durable. As mentioned with rubies, corundum is second only to diamond for hardness. The majority of corundum found is used for industrial purposes.

Because of its sturdiness corundum lasts long after other sediments wear away. Since it is dense, it tends to be found in placer deposits (where erosion and gravity have essentially sifted the heavier bits and pieces together into a gravel over the millennia) and alluvial deposits (where water washed away the original sediment).

For traditional blue sapphires, value is determined by the color of the stones-how pure, how vivid, and how dark. Generally color wise the bluer the better. The blue color comes from traces of titanium and iron.

Monatana’s Yogo sapphires come in a wide range of colors.

 

A small amount of purple secondary hue is considered acceptable, and if subtle enough, can even raise the value of the gem. Vanadium is the coloring element that brings purple and violet (and orange!). Any trace of green (a smaller iron content) lowers it vastly. (I don’t know why, sounds like it’d be a lovely color to me!) Likewise, the richer and more saturated the color the better.

Depending on who you ask the most preferred shades are either an almost primary blue or a slightly lighter rare cornflower blue found in a small part of the Himalayas.

Recently a pink-orange sapphire variant known as padparadschah (chromium and vanadium) sapphire has gotten very popular.

Traditionally sapphire has symbolized loyalty, faithfulness, sincerity and truth. The richness of its color keeps it associated with nobility and royalty. And despite its myriad of shades, it is first and foremost the blue to which every other gem is compared.

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A Gemstone of the First Water (And no, not diamonds)

 

An enormous aquamarine crystal and Dom Pedro – the gemstone cut from it.

Aquamarine is the traditional birthstone for the month of March.

 

Aquamarine means seawater. It’s the perfect name, since the stone ranges from pale green to middle blues. The shade depends on the how much of different forms of iron impurities the stone has. (A different iron produces yellow and a combination makes a dark blue!)

 

Compared to emerald, it’s a relatively common form of beryl-it’s found all over the world, but most gem quality stones come from Brazil.

 

Pale aquamarines can be confused with many other types of gems.

 

In the 1740s a huge diamond was mined in Brazil. It became the property of the Portuguese royal family-the Braganzas. This Braganza Diamond vanished. Some believe it was cut into much smaller gems and set in the crown jewels. In this case the famous diamond might have been a particularly brilliant aquamarine or white topaz. (Apparently the reports can’t even agree on what color the diamond was-famous, but poorly reported!)

 

There’s a beautiful carved aquamarine, also of Brazilian origin, just recently acquired by the Smithsonian Museum of Natural History. It’s known as the Dom Pedro and is 14″ long and almost 5 lbs.

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Turkish Blue

Tree of turquoise chips with sterling silver and copper.

Tree of turquoise chips with sterling silver and copper.

Turquoise is one of December’s traditional birthstones. (As designated by the American Gem Society. The other two are zircon and tanzanite.)

 

To me it’s such a summery color. I guess on the right winter day you can have a turquoise sky brilliant against the snow and bare trees.

 

Turquoise supposedly gets its name from the middle French for Turkey, since the trade routes that first brought turquoise to Europe came through that country.

 

It’s an opaque stone with a texture somewhere between waxy and glassy. It takes polishing well but is relatively soft. (Mohs 5-6) The color can change with exposure to cosmetics, oil, sweat and detergents as well as bright light. Turquoise seems to be another of those stones that is popular for rings but probably shouldn’t be used for them! At least take them off before washing your hands.

 

Turquoise is a secondary mineral; it forms when acid solutions leech elements from other minerals. It doesn’t have a crystal shape, so tends to form clusters or nodules in veins and often grows with other copper related minerals. (For example, chrysocolla or malachite. Great color combinations.) The blue in turquoise comes from the copper, and the green hints from iron and chromium.

 

Turquoise is one of the most ancient gemstones; it has been mined for at least 5000 years. The mines in the Sinai were already worked out by 2000 BCE! (And people have been making imitations almost as long. The Egyptians had faience, a type of pottery glazed in a turquoise color.)

 

In the states we tend to associate turquoise with the Southwest. In a lot of places it’s a lucrative secondary to copper mining. Apparently the classic Southwestern silver and turquoise jewelry is a fairly modern phenomenon. Supposedly the concept was pushed by traders in the 1880s. Before then Native Americans used turquoise in solid beads, mosaics and carving rather than settings.

 

Some of the turquoise minded in the southwest is still gem quality (especially the Sleeping Beauty and Kingman mines), but a lot of it is treated to get it stable enough to use.

 

It’s kind of frustrating, because it is hard to tell if material sold has been dyed or stabilized with plastics or epoxy. On the plus side, it has also led more recently to a type of stabilizing/reconstituting that adds brass or copper veining through the stone. It doesn’t make any pretense at being natural and is a lot of fun to work with!

 

The best imitation is called Gilson turquoise. It has both uniform color and veined variants. The most common way to fake turquoise is to dye naturally white stones that possess similar textures (and veining patterns).

 

Value for turquoise seems to be very much in the eye of the beholder. Some hold out for the most turquoise of the turquoises with very uniform color-the best quality of this type comes from Iran and is the most desirable in the middle east and much western jewelry.

 

Others prefer the stone to have a cob webbing of matrix when the pattern and color is complimentary, emphasizing the richness of the color. This is the type generally preferred by artists in the Far East as well as by many Southwestern artists.

 

Oh, and apparently there’s a Turquoise Museum in Albuquerque, NM. Who Knew?

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Gems underfoot

I loved Ann Hinde’s display for the International Flower Arranging show’s mineral theme when I saw it this summer. It was inspired by an amethyst geode.

Amethyst is a popular stone, one of very few naturally occurring fully purple gems. It is the traditional birthstone for February. Amethyst is a variant of quartz. Iron impurities give it those beautiful shades of purple. Regarding its famous color-if you run across prasiolite, sometimes called green amethyst, just be aware that it’s most likely heat treated or irradiated. (It’s not an issue, so long as you know and aren’t being told or charged for the natural gem. They are a lovely mint green, it’s just that the natural stone is extremely rare.)

geode with amethyst pendant

Geodes are partially filled hollow cavities in rock that are lined by minerals. Their name comes from the Greek for earthlike. (As in Gaia.)

One example of a geode would be a gas bubble in lava. That hollow stays and over time solutions containing dissolved minerals can filter in and leave deposits within the hollow, often resulting in layers of agate and then layers of quartz and/or calcite crystals.

Studying the order of the layers can give a window into the geologic history of the area in which the geode is found.

I like working with slices of geodes because you get to see that external skin and the swirls of agate layers as well as the sparkling crystals.

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