Moonstone cabochons in a jewellers window
Moonstone cabochons in a jewellers window (Photo credit: Wikipedia)

A stone that seems to capture the soft light of the moon: what could be a better gem for a fantasy novel? There’s something romantic about this jewel whose sheen evokes moonlight or captive spirits.

Moonstone is a type of feldspar, a large group of aluminum silicates that compose about half of the earth’s crust and are also found in meteorites and on the moon. Feldspars provide a number of minor gemstones, including sunstone, labradorite, amazonstone and a few others. Like the garnet and tourmaline mineral families, feldspars occur in various solid solution series where, say, you can find a pure potassium member on one end and a potassium-sodium variant on the other and any intermediate mix in-between. The primary moonstone mineral is orthoclase but the sodium rich sister of orthoclase called sanidine also produces moonstones.

As with almost all feldspar, orthoclase is typically opaque, often with extremely large crystals. There are reliable reports of opaque crystals up to 30 feet long and stories, which may have some truth to them, of even larger crystals. Occasionally, crystals are transparent or translucent, although these are much smaller. Clear ones can be cut as a gem, often yellow or pale brown. When minute intergrowths of sodium- and potassium-rich feldspars form, the play of light on the layers can produce adularescence: the moonstone effect.

Orthoclase,moonstone (Photo credit: Wikipedia)

Adularescence (from French after the Adula mountains in Switzerland, related to feldspar deposits there, I believe) is a soft white to bluish sheen. As the stone is turned in the light, the sheen can move around and deepen or vanish. This is a beautiful but subtle affect, appropriate for something named after the moon.

The Roman Pliny the Elder (23-79 CE, killed in the eruption of Vesuvius that created the Pompeian ruins) recorded a stone he called an asterion, which most authorities believe was a moonstone, not a rayed-gem like a star sapphire. He described it as “a colorless stone…[from India] having within it the appearance of a star shining brightly like the full moon.” (Courtesy Glimmerdreams.)

The stones are fairly soft, 6 to 6.5 on the Mohs scale, which means common household dust can scratch it. Those with good adularescence are cut en cabochon, usually as a hemisphere or hemi-oval, but sometimes polished as beads or irregular stones. Quality varies from cracked, cloudy, and barely shimmering to ethereal. Naturally, the best quality material is somewhat rare and expensive. Most of what you’ll find on the low-end is not very attractive so beware of those “great deals” on eBay. Stones can be white, champagne colored, or bluish. Online, you can find other colors, although I’m not sure if they are treated or artificial.

The link to the heavens, captured starlight or moonlight, the magical sheen, all might make this a great jewel for a fantasy novel. It can be used simply as an attractive, non-magical stone (perhaps mistaken as magical) but there’s quite a wide range of fantastic options: from a container for captured light, like Galadriel’s Phial, to a repository for a spirit, soul or ghost. The sheen intensity or glow could also be linked to certain occurrences (time of day, presence of a moon, presence of evil or ghosts, etc.) Perhaps, the stones can be used as a ‘trap’ to catch a soul or ghost, or similarly, hold such a spirit that could be communed with or used to power diabolical magic.

Garnets: much more than a red gem

English: Collection of loose cut Garnet gemstones.
English: Collection of loose cut Garnet gemstones. (Photo credit: Wikipedia)

Continuing in the gemstones for fantasy writers series, let’s look at versatile garnets. If you aren’t too familiar with garnets, you may think of them as dark, sometimes brownish and relegated to Victorian jewelry but there’s much more to them.

As with tourmaline, garnet is a family of minerals with similar structure, in this case a silicate of the form X3Y2(SiO4)3, where X can be calcium, ferrous iron, magnesium, or manganese; and Y can be aluminum, ferric iron, chromium, manganese, silicon, titanium, zirconium or vanadium. Wikipedia lists 27 different minerals classified as garnet but only about 5 varieties are typically used as gemstones. Garnet is generally formed in heavily metamorphized rocks like schist as it takes a lot of heat and pressure.

English: Fragments of Rhodolite Garnet crystal...Garnet is quite common- I’ve found alamandine in gravel in the Adirondacks in New York and as to be expected with so many minerals in the family, it can be found all over the world. As a gemstone, it comes in almost as many colors as tourmaline, except for blue. However, it also doesn’t show tourmaline’s tendency for multiple colors in a single crystal. Crystals are “chunky” rather than long prisms and range from dodecahedrons to trapezohedron to a mix of the two. Garnet is a bit softer to a bit harder than quartz and is sometimes used as an abrasive.

Pyrope and almandine are the garnets that most readily come to mind. Bohemia provided much of the garnet used in Victorian jewelry. It was dark red, sometimes brownish. Very dark stones are sometimes lightened by being cut en cabochon with the back hollowed out. These days, these two varieties are commonly used for beads or for lower end jewelry except for rhodolite: this quite pretty pink to purplish garnet is mid-way between Pyrope (which is Mg3Al2(SiO4)3) and Almandine (which is Fe3Al2(siO4)3), that is, it is a solid solution of the two Magnesium and Iron varieties.

Tsavorite (Photo credit: Wikipedia)

One of the most popular varieties of garnet is marketed as tsavorite (or tsavolite in Europe), a green form of grossular garnet which has become very popular for its clarity and sometimes emerald-like color.

In the fantasy world, it is probably best to stick to red garnet, since that is what most people will think of. For instance, rather than use the green tsavorite, you  might just want to stick with emeralds (and I’d recommend staying away from the term tsavorite since that comes from an African place name and may seem to be a bit of an anachronism to some readers.)

Sutton Hoo - Anglo-Saxon slider
Sutton Hoo – Anglo-Saxon slider (Photo credit: Kotomicreations)

But within the realm of red, garnet make can make for an interesting stone to sprinkle in native rocks- say the walls of a dungeon. For idols, it could provide a deep, red stone if you didn’t want to go with something as valuable as ruby. Similarly, for jewelry it might be suitable for lower nobility or merchants. As a reasonably cheap stone, it could also serve for warrior’s gear (where it would not break the bank if damaged). In fact, one of the most striking use of garnets was in Anglo-Saxon jewelry where it was cut as slivers used for in-lay, such as some of the spectacular Sutton Hoo pieces. Glass enamel has also been used for a similar effect.

Like most gemstones, synthetic material is available, with some variants not found in nature such as YAG used in lasers. Perhaps in a science fiction setting, you could extrapolate still more exotic garnets.

Gem Messages

A classic in line bracelet by Trifari. This st...
A classic in line bracelet by Trifari. This style become known as a tennis bracelet. (Photo credit: Wikipedia)

George Eliot said These gems have life in them: their colors speak, say what words fail of. It is possible to make gems really speak by carrying a message.

Gems have adorned many a story and many a leading figure but there are other uses for gems. The rich, especially those with a guilty conscience (think dictators and crime bosses) are known to keep small cases of diamonds on their person at all times, not for aesthetics but as a ready source of wealth in exile. Fancy colored diamonds, even ones that are rather ugly, serve as a highly portable, compact source of wealth: a cigarette case might hold ten or a hundred million dollars in diamonds, if they are the right type of diamonds. When you hear of the latest outrageous price per caret of a blue or red diamond, it is almost certainly on behalf of a very rich person that wants to turn a lot of money into a discreet form.

There’s much more one can do with gems though. This post deals with real-world physical properties of gems that might be of use in a story. Most of these ideas are probably better suited for a contemporary thriller or science fiction but some might be of use in fantasy.

Consider means of encoding information with gems. Many of you may already be aware that some diamonds have microscopic serial numbers inscribed on them. These can be used to identify them after a theft or to mark their origin (to avoid “blood diamonds” for instance.) Nothing says the information has to be a simple serial number though: one could inscribe any short message on a diamond or other gem stone, from a security key to an incriminating message. Or perhaps someone has used the serial number on their diamond as their security key?

But physically inscribing a gemstone is just one of many ways to store information with gems. One could take advantage of colored stones or even the names of stone to encode a message in a tennis bracelet. For instance, the color of a gem could be assigned an ordinal number from the colors of the rainbow (old Roy G. Biv: Red, Orange, Yellow, Green, Blue, Indigo, Violet). Seven colors for seven numbers could serve to encode a combination key or any number in base 7 (an odd base to use but converted easily enough to more common base 10.) Other color encodings can exist. Or the encoding might rely on the name of the gems: sapphire for S, Ruby for R, etc. This could result in a rather garish (and obvious) bracelet though. Thankfully, there are more subtle encodings available.

More subtly, one can use facets to encode information. It would be tricky and require a good stonecutter (thus creating a lead for a sleuth) but one can modify standard cuts. A standard round brilliant cut diamond has 58 facets but a good stone cutter can omit or add facets. This could be in a fairly obvious manner, such as a missing facet so that anyone with a loop might notice the omission or it could be done as a variation of the brilliant cut that might require more careful analysis (57 properly spaced facets rather than 58 might take careful work to notice). You could alter a specific facet for a binary encoding (standard brilliant, altered brilliant) but with 58 facets to play with you could encode a lot more information into a single stone depending on how much you wanted to affect the look of the cut stone. However, alter the standard cut too much and even a novice might notice it.

A rough specimen of cordierite, showing dichro...
A rough specimen of cordierite, showing dichroism (left); a cut stone (right) (Photo credit: Wikipedia)

Beyond names, colors and shape of the stone there are still more properties to work with. Pleiochroism is an optical property that changes the color of a stone depending on the axis through which it is viewed. Most gemstones exhibit this property but you  may be unaware of it as any good stonecutter knows about this and takes advantage of it. In many gemstones, the color change is more a matter of intensity: some sapphires for instance are more intensely colored along the axis of gem growth and weakly colored perpendicular to that axis. Therefore these stones are cut so the face is along the axis to deepened the blue (or other color for fancy sapphires). But sometimes a stone can be too dark and the color could be lightened by cutting against the axis.

However, there are some stones that actually display a different color depending on the angle of viewing. Iolite (water sapphire) is a well-known stone with strong pleochroism. It can show blue or violet depending on the angle. It’s also a pretty cheap stone if you want to go to eBay and buy one as an example.

With simple two-axis pleochroism, you could encode a message on a strand of Iolite beads, with some beads cut on the blue axis and others cut on against the blue axis. Then you would have alternating blue and violet which could be a binary encoding. Of course, this isn’t terribly interesting since you could do the exact same thing mixing sapphires and amethyst (or purple sapphire) beads. But there is also trichroism: gemstones that show three different colors depending on how you view them.

Tanzanite is known for its beautiful violet-blue color but one stone can show blue, violet or red depending on the axis. One could imagine a tennis bracelet of carefully selected tanzanites that straight on shows violet but when viewed from the side show blue or red depending on how the stone is placed in the setting, resulting in another binary encoding. If you wanted a really tricky code, you could actually use the blue/red dichroism to encode a rotation (probably using some quanta related to the number of facets in the crown) instead of just a binary value. This would make it very hard for someone not in the know to realize there is an encoding on the bracelet. Quite diabolical.

Another gem property that can carry a hidden message is fluorescence. In some gemstones, there is a wide variation in whether a given specimen fluoresces or not. Diamonds are one such stone where it is used to prove the authenticity of famous jewelry pieces. Some diamonds fluoresce blue or yellow, some show little or no fluorescence, even if in normal light they all might look identical. Back to our handy tennis bracelet: by selecting fluorescent and non-fluorescent stones, one could create a binary (or higher base if one makes use of a range of fluorescent colors) message, one that is only visible with a UV light.

These are all different ways I can imagine that a spy or unwitting socialite was carrying a message on his or her person. Maybe daddy doesn’t give a damn about his daughter, he just wants that tennis bracelet off her wrist because it is the key to his Swiss safe deposit box!

Most of these techniques require modern scientific methods to use or at least an understanding of physical properties that might be out-of-place in a fantasy novel but they might make for a nice twist in a modern mystery or a science fiction novel.

Gems are one of my minor hobbies and I will be following up this post with some additional ones on specific gems. If you have one you are particularly interested in, let me know in the comments and I’ll see if I can get to that one first. Otherwise, I will probably start with garnet and tourmaline, both secondary stones with a wide range of colors and properties.