Birthstones: Moonstone (June)

I'm not going to beat myself up over how long it's been since a birthstones post, but I'll just say: I got busy! But now I have a little more time to talk about rocks again!

As I mentioned on Twitter a few days ago, June has a lot of associated birthstones with it. The original 1912 Kansas City list, for whatever reason, came up with two stones for half of the months. When they updated the list in 2002, June and December each had three. And since the Tiffany & Co. list gives agate as June's birthstone, that leaves June with a whopping four (!!) birthstones. I've covered three of them already: alexandrite, agate, and pearls. Now for the remaining gem: moonstone!

Moonstone is a feldspar, a kind of silicate mineral that crystallizes out of magma. Feldspars are the most common minerals in the Earth's crust—after that is our old favorite, quartz. Both are silicates; the difference between feldspars and quartz largely comes down to the presence of potassium, aluminum, and sodium in feldspars.

Moonstone in particular has alternating layers of two different kinds of feldspar: albite and orthoclase.

Orthoclase, courtesy Archeodontosaurus

Albite, courtesy Rock Currier

The alternating layers of these minerals (or rather, the space between these layers where light can bounce and play) is what causes moonstone's distinctive sheen, schiller.

The other great example of schiller in gemstones is labradorite (also a feldspar):

The difference between moonstone and labradorite, structurally, seems to come down to ingredients. Labradorite contains sodium, calcium, and aluminum (in addition to silicate), while moonstone contains just potassium and aluminum (in addition to silicate). They also have different refractive indexes and specific gravities.

You can find labradorite that looks an awful lot like moonstone. Rainbow moonstone, for example, is technically labradorite (but no less stunning for the misnomer).

Rainbow moonstone cabochons from Coyote Rainbow

It's very easy to see why moonstone's milky white inner glow would have it associated with the moon. Its use in jewelry dates back to ancient cultures, where they were believed to be the solidified rays of the moon. (The Internet attributes this belief to Rome as well as India.) As with other moon-related objects, moonstone was quickly associated with emotions and romance, female fertility, and lunar deities. Oddly, it was also associated with protection during travel—perhaps because of the moon's connection with water. It was also believed that if you held a moonstone in your mouth during a full moon, you could see your future.

More recently, moonstone became popular during the Art Nouveau movement. And after America's space obsession in the 1960s, it became the official state gem of Florida (home of the Kennedy Space Center in Cape Canaveral).

As moonstone is relatively soft (a 6 on the Mohs scale), it should be treated with care. If you need to clean a moonstone piece, use warm water and a soft brush. If that's not enough, add just a touch of mild detergent. Avoid using ultrasonic cleaners—this may damage the stone due to moonstone's natural cleavage and cracks. Be careful about storing them alongside harder stones, like rubies, diamonds, or garnets. Extreme changes in temperature might also damage moonstone.

Avogadro's number in moonstone and black banded agate by Kokoba

Birthstones: Bloodstone (March)

If you're a March baby and aquamarine isn't really your bag, you can claim bloodstone instead! It was once known as heliotrope, but these days heliotrope is more associated with the pinkish-purple flower than the green and red mineral.

I've finished the entire "modern" list of birthstones. But there are so many more left! There's the earlier Kansas City list, the British Goldsmiths' list, and the original Tiffany & Co. list to go through, not to mention astrological associations. First, though, we'll finish up both of the Kansas City lists.

Who in this world of ours their eyes
In March first open shall be wise,
In days of peril firm and brave,
And wear a bloodstone to their grave.

The old name of heliotrope refers to Greco-Roman ideas about the relationship between stones and the sun ("helio" being sun and "trope" being to turn). It's unclear when people started referring to the stone as "blood jasper" and then "bloodstone," but it probably began in the Middle Ages in Europe. As the story goes, the blood from Christ's crucifixion stained green stones that were at his feet, creating the first bloodstone. 

Unsurprisingly, bloodstone was also associated with martyrs as well, sometimes called "martyr's stone." It was a popular choice for gemstone engravings depicting martyrdom or the crucifixion. It was also a popular stone to use for signet rings and seals. 

"Christ at the Column,"  17th Century Italian

Bloodstone is a silicate, like so many other stones, so it is primarily built out of SiO4. The base green color comes from inclusions of chlorite and amphibole within the silicate; both of those minerals are green due to a variety of elements: lithium, magnesium, or iron in conjunction with aluminum and hydrogen. The orange-red flecks of "blood" are due to iron oxides (such as hematite). 

Chlorite

Amphibole

But the association of blood with bloodstone has been around for longer than the Middle Ages. In many cultures, including India and Babylonia, it was believed to stop bleeding and thus was a popular stone for warriors to carry. Likewise it was thought to help with anything related to blood and its circulation, including venomous animal bites and aphrodisiacs.

Bloodstone is lovely but not prohibitively expensive. There are large sources in India, Australia, South Africa, and the US (to name a few), so there isn't much of a market for synthetic or fake bloodstone. However, bloodstone can often resemble jaspers, particularly fancy and ocean jaspers, so there can be improperly identified stones here and there.

Fancy jasper

Ocean jasper

Bloodstone

See what I mean?

The difference between them is, arguably, quite fine (on the ontological, philosophical level). The biggest difference is in their formation: jaspers are a sedimentary aggregate of a whole bunch of different things, while chalcedony (which is the mineral group bloodstone belongs to) is primarily a silicate. You can see the difference under a microscope: a jasper is microcrystaline while chalcedony is cryptocrystaline (this means that jasper has a slightly larger crystal structure and doesn't require as much magnification). Bloodstone should always streak a reddish brown in a mineral streak test, whereas a jasper might be brown, or it might be other colors.

Ideally, a bloodstone should be consistently green except for "splatters" here and there of red-orange, though sometimes there are streaks instead. If you are seeing bits of mauve, blue, or purple mixed in, it's likely a form of jasper instead of bloodstone. If it's green but the splatters are more yellow than red, that's known as "plasma." Bloodstone is very rarely color-enhanced, though like other stones it often has a finish that can be damaged by harsh detergents; like other stones, it should be cleaned with warm water.

Birthstones: Turquoise (December)

If cold December gave you birth,
The month of snow and ice and mirth,
Place on your hand a turquoise blue;
Success will bless whate'er you do.

According to the Kansas City list, December has a few choices (turquoise, blue zircon, tanzanite; lapis lazuli prior), but we'll start with turquoise.

Turquoise is a secondary mineral; instead of forming under heat and pressure like silicates, diamonds, or corundum, it's the result of weathering and oxidation on copper deposits. Its chemical formula is CuAl₆(PO₄)₄(OH)₈·4H₂O, making it a hydrate. On a microscopic level, turqouise looks something like this:

If you want to peek at most of the modern Kansas City birthstones under an Internet microscope (metaphorically), this Japanese website (in English) has a really handy list!

Turquoise forms in arid regions with histories of volcanic activity, and because its formation is highly irregular, the stone can vary significantly in its color and characteristics. Thus, it's become common to refer to turquoise by its mine or place of origin, as turquoise pieces from the same mine share similar characteristics.

Sleeping Beauty Turquoise

Kingman Turquoise

Bisbee Turquoise

Turquoise is one of the oldest precious stones known to civilization and was found and used all around the world, even in ancient times. The ruling classes in pre-Columbian Mesoamerica, Egypt, Persia, Tibet, and China (just to name a few) used it as adornment and often as a magical talisman or good luck charm. The oldest known turquoise mine was operating in Egypt as far back as 5500 BCE.

The English word turquoise comes from an Old French word for "Turkish," turqueise. World-renowned for thousands of years, turquoise nonetheless did not make its way to Europe until well into the Common Era via Turkey, though the stone itself originated in mines in Iran. Other, older names for turquoise include callais (according to Pliny the Elder), pirouzeh (Persian, "victory/victorious"), firouzeh (Arabic), and teoxihuitl (Aztec).

Since it's such an old stone, traditions and beliefs about turquoise abound. In Ancient Persia it was believed to be a talisman against, and also a harbinger of, death: it was worn for protection, and a change in the color was believed to be a warning of imminent doom. Turquoise can absolutely change color, but this is the natural result of exposure to radiation (even just sunlight) or chemical reactions with cosmetics, perfumes, or the oils of the skin.

The Zunis and Apache tribes in the New World also sported turquoise. According to Apache lore, turquoise improved aim. The Zunis believed that it improved a horse's sure-footedness and prevented the rider from being injured from a fall or throw.

Turquoise is a soft, porous mineral—about a 6 on the Mohs scale. It can absorb perfumes and scents very easily; if turquoise is going to be part of your ensemble on a night out, apply any perfumes/hair sprays/etc. before putting on your jewelry. Do not store turquoise in airtight containers (like opal, it needs some ambient moisture), and be careful not to leave it with particularly malodorous items, lest it pick some of it up. It is also very susceptible to the solvents used in most cleaning solutions; instead, it's best to clean turquoise with a soft toothbrush and plain water.

Because turquoise is so soft, it often undergoes treatments to increase its hardness and durability. These include waxing and oiling (using wax or oil to fill the natural fissures of the stone), backing (using adhesive to attach a thin slice of turquoise to a more durable back), and stabilization (similar to waxing and oiling, but using an epoxy or sodium silicate instead). Dull pieces are often dyed with Prussian blue to enhance their color. Gemologists can determine what treatment a stone has been subjected to, but those tests are often destructive (ruining the color of whatever portion is tested). There is also reconstituted turquoise: flakes and turquoise powder useless on its own combined and suspended in a resin. This often referred to as "block" turquoise, or sometimes just "block."

Naturally, turquoise being so popular, it is often imitated. Not all reconstituted turquoise contains any turquoise at all: often, block turquoise is nothing but resin and dye. Howlite, a white, porous stone with gray veins, is often dyed to resemble turquoise. Some stores are up front about this and some are not. I've also noticed that people on Etsy will tag anything veiny and light blue as turquoise, though if you read carefully it's "turquoise variscite" or "teal howlite" or whatever. Read those item descriptions carefully! And there is no such thing was "white turquoise": I suspect that's a sexed-up term for howlite.

Birthstones: Topaz (November)

Who first comes to this world below
With drear November's fog and snow,
Should prize the topaz's amber hue,
Emblem of friends and lovers true.

Like most other birthstones, the topaz is a proper silicate; it's primarily made out of SiO₄. It forms in igneous rocks high in silicate (pegmatites, granite, etc.). Like other tough silicates (ruby, for example), topaz is often what remains after weathering. As a result, topaz is often found in gravel and/or alluvial deposits. Significant sources include Brazil, the Ural mountains, Sri Lanka, and Burma.

What separates topaz from quartz is aluminum and fluorine that hang about in between the tetrahedrons of silicate. Its proper chemical formula is Al₂SiO₄(F,OH)₂.

However, aluminum and fluorine don't necessarily affect the color of topaz, since it can form without colors. They instead affect the crystal lattice: topaz is orthorhombic in shape, while quartz is trigonal.

Trigonal

Orthorhombic

Stray chromium creates red, pink, and purple topaz; flaws in the crystal structure can lead to yellow, brown, or blue coloring. As a result of this play of light within the crystal structure, topaz is often pleochroic. There is also a whole host of trade names for topaz: imperial topaz is yellow/pink/pink-orange; blue topaz (which is rare in nature; most blue topaz has been dyed, heated, or otherwise enhanced), mystic topaz (colorless topaz given an iridescent coating), and orange topaz (orange to orange-yellow). Only the orange/orange-yellow variety are considered November's birthstone. ("Traditionally," anyway. You do you etc. etc.)

128 ct topaz from HandyNat

The name topaz is generally believed to refer to an island by the name of Τοpáziοs/Τοpáziοn in the Red Sea. Now called Zabargad/St. John's, it was an ancient site for yellow gemstones (that are now believed to have been a variety of peridot rather than true topaz) and, like many other stones, the name of their place of origin became a shorthand term for the gem itself—or any gem similar to it. Writings in the Middle Ages used the name topaz to refer to any yellow-colored stone, so it's hard to say precisely when topaz (versus olivine peridot or citrine quartz) was discovered. It isn't exactly hard to find, in any case; it's been with us for a while.

The ancient Greeks believed that topaz—and any other yellow-colored stone—imbued a person with physical strength. The Romans thought it improved eyesight, and Egyptians would wear it as a general stone of protection. Topaz was also used in Vedic astrology (some assert that the name doesn't come from the island of Topázios but the Sanskrit word "tapas," meaning fire). In addition to being associated with Jupiter, a topaz worn near the heart was thought to bestow long life, beauty, and intelligence. Europeans in the Middle Ages believed topaz could break curses and dispel anger.

Because it is relatively tough (8 on the Mohs scale), topaz can also be used as an abrasive,  but beyond that, topaz is prized first and foremost for its beauty.

Birthstones: Opal (October)

October's child is born for woe,
And life's vicissitudes must know,
But lay an opal on her breast,
And hope will lull those woes to rest.

 Opal is a really fascinating gemstone, both in appearance, composition, and history. You can pick it out right away by the brilliant play of color that is the trademark of (one of) October's birthstones:

One reason that opal is particularly interesting is that it's the first birthstone in this series to not be a proper mineral.

A mineral has a uniform, organized structure throughout the entire specimen. One bit of a mineral looks largely like the next. Quartz is Si04 all the way through, ruby and sapphire are Al203 all the way through, and so on.

Opal is classed as a mineraloid—as being almost a mineral. It does have bits and pieces of regularity, but they are not found overall. Instead, an opal's crystal structure (such as it is) is akin to marbles in a vase: globs of order and structure (silicates) with bits of empty space in between. As it is hydrated, some of those gaps in between the marbles are filled with water. From 6%–10% of a given opal's weight may consist of water, though it can be as low as 3% and as high as 21%.

It is the space between that is the opal's favorite Dave Matthews Band song creates the brilliant play of color so renowned in opal. That space distorts and bends the light, resulting in a variety of different colors. You can think of an opal as an aggregate of lots of little prisms.

Microscopic silcate beads in opal.

The name "opal" likely can be traced to the Sanskrit word upala, meaning "precious stone." It comes to us today from Sanskrit to Greek (opallios, now meaning "color change") to Latin (opalus) to Middle French (opalle) to English. Because of the multitude of colors found in it, opals were thought to be comprised of many other precious gems, as Pliny the Elder wrote:

Made up of the glories of the most precious gems, to describe them is a matter of inexpressible difficulty. For there is amongst them the gentler fire of the ruby, there is the rich purple of the amethyst, there is the sea-green of the emerald, and all shining together in an indescribable union.

Opal was a popular stone among blondes, as it was thought to be a remedy against darkening hair. It was an opal ring that granted invisibility in the tale of Gyges, and thereafter in Western thought it was associated with invisibility.

Something like 97% of the world's opal supply comes from Australia, and the stone has long been treasured by Aboriginals. They associated the stone's rainbow flashes with their creator god (who originally came to Earth on a rainbow) and outcrops with opal became sacred ceremonial grounds. However, those were not the opals that Pliny the Elder was writing about; early sources in Europe often came from what is today Hungary, and then from Central America once the Age of Exploration was well underway. The world's earliest opal artifacts (dating to 4000 BCE), meanwhile, were found in Kenya, with opal from Ethiopia.

For a short while, opals were considered an unlucky stone, thanks in large part to Sir Walter Scott's 1827 novel, Anne of Geuerstein. One of the main characters, Lady Hermione, wore a beautiful opal in her hair whose color change matched her mood. After meeting some holy water, both Lady Hermione and the stone became nothing but ash.

This image lodged itself in the popular consciousness and the market for opals plummeted. This decline wasn't helped by the fact that people at the time had no idea how to properly care for opals; more than other precious stones, opal was prone to cracking and breaking, always interpreted as an ill omen.

But opal's beauty is hard to resist. With the discovery of beautiful black opals in Australia in 1877, the market revived. Shortly thereafter, Australia overtook Hungary and other European suppliers as the world leader in opal production.

I'm writing about opal in a general sense, but there are many different types of opal. There isn't any particularly type of opal that is specifically the birthstone and there isn't too much difference between types beyond coloration.

There is white opal, the most common kind of opal. At a distance, it looks more or less white (except for any color play). White opal accounts for about 60% of the world supply of opal.

There is black opal, which looks much darker at a distance. The play of color on black opal is saturated and striking.

A type very similar to black opal is boulder opal. It gets its name from the ironstone boulders it forms on, and is only found in Queensland, Australia. Boulder opal on its own is quite thin, so it's always cut with a bit of the ironstone boulder left on the back; often there is also ironstone matrix throughout the whole cut stone.

If any of the first two types of opal have unusually transparent bodies, they are referred to as crystal opals.

Outside of Australia, the Mexican fire opal has become popular. Its play of color isn't as dramatic as specimens from Australia, but the colors are often fiery reds, oranges, and yellows (hence the "fire" appellation).

Any kind of opal whose play of color is more subdued and less brilliant than average is referred to as a jelly opal. An opal without any play of color at all is called common, or potch opal. Potch opal comprises 95% of the opal mined, worldwide.

Another cool thing about opal is that it is often a replacement medium for fossils. You often find opal in petrified wood (which is to say, you often find opalized wood) and other fossilized things, including ammonites.

For some reason I never knew this until a few months ago. You learn something new every day, or something.

Because the most beautiful opals command high prices, there are of course different methods of synthesizing or imitating opal, or just reducing the cost.

If you delve at all into the online opal mines you will find people discussing doublet and triplet opals. These are slim pieces of opal epoxy'd on to a backing: sometimes potch opal, sometimes another darker, sturdy stone, sometimes black glass. This is a doublet (as in two layers, or double). A triplet is a doublet with a dome of quartz affixed to the other side of the opal—3 layers. This has long been a common way for people to create affordable, opal-like jewelry.

Opal has been synthesized since 1974, and the practice continues today, Lab-grown opals can be distinguished from natural ones by their play of color (it is much more regular and symmetrical, with larger color bands, in lab-grown than in nature). Natural opals also fluoresce, while lab-grown ones do not.

 Many, though not all, synthetic opals are more properly called imitation, as they contain ingredients not found in natural opals (plastic stabilizers, primarily). An even lower-budget imitation opal is just colored foil under glass. This was a popular choice for costume jewelry, especially during the Art Nouveau movement.

Opals also require some more care and attention than other birthstones. They benefit from lots of contact with skin, as they are hydrated mineraloids; without periodic exposure to moisture, they tend to become brittle and crack easily. They are also sensitive to sudden changes in temperature or humidity. Solid opals are not damaged by being submerged in water, but this should be avoided with doublets and triplets.

There are some misnomers out there in the world. "Opalite," for example, is not opal but is a glass imitation with similar play of color. "Sea opal" is merely sea glass. "Slocum opal" another glass imitation opal, though it less popular these days than opalite. They are all quite lovely, but intentionally marketing them as genuine opals is a pretty crappy thing to do.

Birthstones: Sapphire (September)

A maiden born when September leaves
Are rustling in September's breeze,
A sapphire on her brow should bind
`Twill cure diseases of the mind. 

After our brief trip back into silicates with peridot, in September we're returning to corundum. Instead of silicon and oxygen, it's composed of aluminum and oxygen.

Then what's the difference between a ruby and a sapphire? What makes them different colors? Chemical impurities. Ruby contains trace amounts of chromium; sapphire contains iron and/or titanium.

("But doesn't iron make things orange-y?" In silicates, yes. Not in oxides. This is the same reason why chromium makes silicates look green, but ruby red. It forms different kinds of bonds that reflect or absorb light differently.)

A cool effect you can get both in rubies and in sapphires is a "star": a rutile (titanium dioxide) crystal forms within the gem and creates a 6-lined star shape. This affect is called "asterism." It's fairly rare in nature, but it's possible to induce this effect in lab-grown sapphire.

The name sapphire has a complicated history. The origins of its name can be traced conclusively to the Hebrew sappir, but it is likely even older than that. That became the Greek sapheiros, which was simply "blue stone." Such a precise name meant that many ancient blue stones were also called sapphire. Lapis lazuli, for example, was often referred to as sapphire, while sapphire might have been called hyakinthos by the ancient Greeks. There is another school of thought that suggests the name comes from Sanskrit sanipriya ("precious to Saturn"). It's difficult to say when, precisely, the name sapphire was pinned down to Al2O3.

Of course, as we learned with rubies, sapphires can come in a variety of colors besides blue.

However, it's the blue sapphire that is most often associated with September and has the most lore associated with it. Al203 in other colors were most likely confused for other stones, or considered separate.

Sapphire is a stone that has been around for a long, long time, as evident by the age of the name, so of course it's picked up a fair amount of folk beliefs and traditions!

Ancient Vedic astrologers believed the stone magnified the positive qualities of Saturn (otherwise considered an unlucky planet): leadership, ambition, responsibility, patience, and longevity. Clergy in the Middle Ages often wore sapphires (or other blue gems) to represent heaven, perhaps creating or just only reinforcing the belief that the stone attracted heavenly blessings. Royalty wore it as a charm against envy. Renaissance thinkers held that the stone could cure anger and stupidity.

The first sapphires were probably sifted out of alluvial (riverbed) deposits, where they are still found today (in addition to underground mines). The largest sapphire producers in the world are Madagascar and Australia. Some of the finest and most famous stones, however, have been mined in Sri Lanka.

Sapphire has also been synthesized since the early 1900s. The process leads to a proper, chemically-identical synthetic stone. Fortunate, because sapphire also has a lot of practical applications; particularly, it can be used for a special kind of glass that can tolerate a heavy heat load and also "let through" a broad spectrum of light. It also is scratch-resistant (considering the only thing harder than it is diamond) and extremely durable. "Sapphire glass" is used in lasers, spectrometers, barcode scanners, those xenon headlights everyone hates so much, and for shatter-resistant windows in armored vehicles. You can also find sapphire in cellphones, emergency vehicle radios, and satellite communications systems. It's quite the multipurpose stone!

Note that there, as always, unscrupulous people intent on trading on the prestige of sapphire's name. I've seen items on Etsy that list "sapphire jasper" as one of their materials used, but that's just a trade name. It's more likely variscite (also known as aqua terra jasper, snakeskin jasper, or impression jasper), which is a beautiful stone....but not actually sapphire. They are related only in that they are pretty.

Natural sapphires are often treated to improve their color and clarity; there are ones that are naturally brilliant and saturated with color, but they are rare and fetch a high price. There are, yes, synthetic ones as well, but beware artificial sapphire (usually just colored glass) posing as the real thing.

Birthstones: Peridot (August)

This is another instance where the updated Kansas City list differs from the original Tiffany & Co. poems. The original Kansas City list in 1912 included the sardonyx from the Tiffany & Co. poem, but also peridot; the updated list dropped sardonyx entirely. Reasons for this elude me but I'm sure they have to do with selling things.

After a brief foray into corundums (corunda?), beryls, and chrysoberyls, with peridot we're back in the realm of silicates: minerals composed primiarily of SiO₄.

Peridot is rich with magnesium (sometimes iron): (Mg, Fe)₂SiO₄. One a microscopic level, the whole thing looks like this:

Peridot, then, exhibits the same characteristics we've come to expect of silicates. What makes peridot unique is that it is always and only an olive yellow-green color. In fact, properly speaking, its full name is peridot olivine—olivine is the larger class of Mg- and/or Fe-rich silicates; peridot is the name given to gem-quality samples.

Where the name comes from is unclear. The first written record of it in English is a 1705 translation of Latin church records from 1245. It might come from the Arabic faridat, meaning only "gem," or it might be a corruption of the Anglo–Norman word pedoretés. The Gemological Institute of America favors the former; the OED favors the latter. Historically, high-quality peridot olivine was often confused with emerald, or sometimes topaz; this is probably why the stone didn't come away with its own name right off the bat. This confusion was rampant in all places and ages, but especially in the treasure stores of European churches. Much like the Black Prince's red spinel (thought to be a ruby at the time), the stones in the Dreikönigsschrein in Köln, Germany were long thought to be emeralds—in fact, they are peridots.

Cleopatra's fabled emerald collection might also have been peridot, but obviously there's no way for us to go back and check.

Needless to say, this green silicate has been around for a while, even if it's operated under many names. While olivine forms deeper in the mantle than most other stones (except diamonds), it is still made of silicate, the most common material in the Earth's crust. One good volcanic eruption can bring a whole host of rough peridot to the surface. Peridot can also form in outer space, on other planets or protoplanets; occasionally they make their way to Earth via a nickel–iron meteorite (called a pallasite). The result is stunning:

The Egyptians mined quite a significant amount of peridot, and used it as a ward against evil and "terrors of the night." It was also thought to treat asthma and reduce the thirst of a fevered person. The stone's power was thought to be enhanced by setting it in gold, stringing it through the hair of a donkey, and wearing it on your left arm.

While it doesn't actually help with asthma, peridot olivine does have other, practical purposes. Right now it is being seriously investigated as a tool in the fight against global climate change, specifically as an agent for sequestering CO2. It's also used in blast furnaces in steel production. On a more frivolous note, olivine is also often used in Finnish saunas as it's fairly dense and also resistant to weathering.

Peridot, while lovely, is not as rare as some of the other stones we've recently looked at and does not typically command jaw-dropping prices. It is also not synthesized either; the only imitation on the market is green glass. 

Birthstones: Ruby (July)

The glowing ruby shall adorn,
Those who in July are born;
Then they'll be exempt and free
From love's doubts and anxiety. 

 Congratulations, July babies, your birthstone is the rarest in all the land!

Ruby is a variety of corundum, a crystalline form of aluminum oxide (illustrated above). It is one of the hardest things on Earth (9 on the Mohs scale), outdone only by diamonds and moissanite. This makes it incredibly useful industrially, in addition to the romance and respect afforded to it in the jewelry world. I mean, let's be real: who doesn't love rubies?

Corundum occurs in a variety of colors in nature, depending on mineral impurities. Ruby is the red variety (from the Latin ruber, meaning "red"), the pink-orange type is padparadscha, and anything else is known as "sapphire." Yes, this includes the sapphire, a stone we'll come to later. In my experience with gemstone names, blue is the default color for sapphire and anything else gets specified in the name ("green sapphire").

Corundum of any kind is relatively rare, as it by definition lacks silicate, one of the most common mineral varieties found in the Earth's crust. While we have some idea of how ruby formation works (magma, granite, marble, and metasomatism are involved), there's not yet a solid hypothesis regarding why marble is so ubiquitous but corundum (usually found within marble when it's found at all) is so rare.

(When I was little, I thought for a long time that "sapphire" referred to a red or yellow color, since it had "fire" right in the name. Considering that there are pink and yellow sapphires, I wasn't too far off....but maybe for the wrong reasons.)

The red in ruby comes from chromium replacing some of the aluminum, resulting in a red color.

But wait! Isn't chromium responsible for green coloring in other stones? How does that work?

Magic.

No, actually: it's complicated. To say that only the replacement of one metal with another results in a color change is disingenuous. Forgive me. That metal has a relationship with the other elements in the crystal, and they both have a relationship with light.

Remember: a gemstone or a crystal doesn't inherently have any particular color. It's all about the reflection and refraction and energy absorbed/not absorbed by a stone in particular, as you might recall from the color shift in alexandrite. Chromium bonds with the silicates in beryl (aquamarine, emerald) differently than it bonds with oxides (corundum), so the light bounces differently and the colors the human eye see as a result are different. You can find a more in-depth explanation at professor Bassam Z. Shakhasiri's chemical of the week feature.

However, corundum isn't the only stone to be called a ruby when it's red-colored.

As I've written about earlier, many of the historical rubies would not be considered rubies today, but rather red spinels. Spinel is not corundum. On a chemical level, spinel looks like this:

while corundum looks like this:

Al₂O₃

Ruby, as in red corundum, has a number of industrial uses. It is sometimes used as an abrasive on metal alloys, in watches and clockwork, and in lasers. When it comes to abrasive, natural industrial-grade leftovers from the mining of gem-quality stones are used. As for time pieces and lasers, synthetic ruby is the stone of choice.

Ruby has a long and storied history in the realm of magic and occult. In Vedic astrology, ruby is associated with the Sun and thought to support one's overall health, vitality, career, wealth, and popularity. More than that, it was thought to render its wearer invulnerable and enable them to live in peace among their enemies, and to bring good fortune in all matters related to the heart. It was also thought to glow with its own inner fire, and to darken in the presence of danger. Small wonder, then, that the Sanskrit name for ruby (ratnaraj) means "king of precious stones." God created rubies first, so the story goes, and then created man to admire it.

Similar beliefs appeared in the West. The Greeks and Romans associated the stone with love, beauty, and affairs of the heart as well as with wealth and riches. By the Middle Ages and the Renaissance, ruby, with all of its associations with love and prosperity. was considered a stone for weddings and to be especially appropriate for wedding gifts.

Because it is such a luxury stone, there is a world of intrigue and misinformation surrounding the ruby. There are any number of synthetic rubies (that is to say, chemically identical but grown in a lab) out there; many of them would require an inspection by a gemologist to distinguish them from natural rubies. Personally, I'm not much of a snob about synthetic stones, since they're chemically identical, often of a higher quality, and not rife with the economic, environmental, and human rights mess that precious gemstones often are. Everyone has different preferences, though!

Besides synthetics, there are also imitation rubies: red-colored stones that are intended to look like ruby. As with other stones, the word "ruby" has gained so much prestige that other stones have acquired trade names like Balas Ruby (red spinel) or Rubellite (red tourmaline). There are even varieties of corundum that lack chromium but have been dyed red to achieve the same color.

It's always been my opinion that there is no point in natural versus synthetic or imitation snobbery; if it looks good, it looks good. Ironically enough, it is the snobbery and obsession with natural stones that leads to the fraud and deceit you see throughout the gemstones market. Don't let yourself get swindled into throwing down a lot of money for some colored glass!

Birthstones: Alexandrite (June)

It seems like I went all of May without a birthstones post. I don't know how that happened!

June is a month where the modern list differs from the original Tiffany's poems and the 1912 Kansas City list.  I'm not sure why it was changed from pearl or moonstone to alexandrite. Perhaps as a way to advertise and sell this rare and expensive stone?

Alexandrite is primarily found in Russia (named after the Russian tsar Alexander), particularly in the Ural mountains, though there are deposits in Brazil, India, Sri Lanka, Madagascar, and Tanzania. It is more properly called chrysoberyl. This might lead you to believe that it has a similar chemical makeup to beryl (which we saw with aquamarine and emerald), but that isn't quite the case. Beryl is softer and contains much more beryllium.

Chrysoberyl: BeAl₂O₄

Chrysoberyl is a beryllium-containing oxide, while beryl is a beryllium-containing silicate. The name "chrysoberyl" comes from the Greek words chrysos, meaning "gold," and beryllus, the Greek name for any hard, lustrous mineral (also later applied to any green-colored stone). Logical, since chrysoberyl is usually greenish-yellow:

Chrysoberyl's formation is a little complicated. It starts with low-density, water-containing magma near the Earth's surface. As the magma cools and forms crystals, the ratio of water to magma increases, as does the presence of rare elements. This water-rich magma ultimately crystallizes later than the other magma, resulting in a pegmatite with overlapping crystals of differing minerals. Chrysoberyl, then, always forms with quartz and is found in granite, marble, and mica schists. However, chrysoberyl is the third-hardest mineral on Earth, after diamond and corundum (which includes ruby and sapphire); often it remains while the other parts of its pegmatite neighbors have eroded away. Then you can find isolated chunks of chrysoberyl in alluvial deposits, gravel, and sand.

Of course, alexandrite doesn't look at all like the typical golden chrysoberyl. Depending on the light (more on that in a minute), it's either green or reddish-purple:

This is because alexandrite is a form of chrysoberyl where chromium has replaced some of the aluminum. If you've been paying attention, you'll remember that trace amounts of chromium in the crystal lattice of a gemstone often results in a green color. This means that for alexandrite to form, there has to be both chromium and beryllium present in the water–magma goop. This does not happen often and as a result the sources for natural alexandrite are quite limited: where there is beryllium-rich "pegmatitic fluid" and chromium-rich rocks.

The color change is due to the human eye and absorbed versus reflected wavelengths of light. The chromium ions in alexandrite are at a sweet spot where in the full spectrum of light (that is, with a balance of red, green, and blue light), the alexandrite reflects a green light, but in incandescent lighting (which is overbalanced in favor of red light), alexandrite appears more reddish. On the one side of alexandrite are rubies and red corundum (which always appear red) and on the other are emeralds (which always appear green). Note that this is a different sort of color change than pleochroism, which isn't related to the type or temperature of the light, but rather the angle at which the light strikes the stone.

Because of its relatively recent discovery (at some point after 1831), there aren't any mythological associations with alexandrite. Chrysoberyl in general (and particularly cat's eye chrysoberyl) was thought to protect the wearer; according to ancient Arabic thought it even rendered a warrior invisible during battle. All varieties were said to help with self-confidence and clarity of thought, and its gold-yellow color was also thought to attract wealth.

"Synthetic" alexandrite is popular, due to the rarity and expense of natural alexandrite. I put synthetic in the scare quotes because properly speaking, synthetic alexandrite isn't a true synthetic (chemically identical but formed in a lab instead of in the Earth), but rather an imitation: corundum or spinels with trace elements to mimic alexandrite's color-changing properties. Some glass imitation alexandrite lacks any color-changing properties whatsoever, but other ones manage to achieve the effect—even without any sort of AB surface coating. 

Alexandrite is one of my favorites, not least because I am a June baby myself. ;) Here are some great alexandrite items I found on Etsy to celebrate!

Amazing Alexandrite

Powered By Toastie Studio - Etsy Tools