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.

Cat’s Eye Gemstones: Chatoyancy

Fine color Cymophane with a sharp and centered...
Fine color Cymophane with a sharp and centered eye. (Photo credit: Wikipedia)

Most folks have seen the tiger’s eye type of cat’s eye and the similar hawk’s eye. This is a silky orange (or blue for hawk’s eye) sheen to a usually opaque stone. More valuable and exotic is a cat’s effect in a translucent stone. There are many gemstones that can exhibit the cat’s eye effect. However, in the gem trade, a cat’s eye stone means cymophane, which is a variety of chrysoberyl. (Another variety of chrysoberyl is the famous color-changing alexandrite. The transparent variety without a cat’s effect is just called chrysoberyl.)

Chatoyancy is the fancy term for “cat’s eye” and literally comes from the French chat (cat) + oeil  (eye) or variously the present participle of chatoyer. The effect is generally caused by very fine crystals within the gem arranged in parallel. The easiest way to visual how this works is to move a spool of shiny thread under a single point light, such as the sun or a bright bulb. The silky sheen on the threads is essentially the same sheen you are seeing off the microscopic, aligned inclusions in a chatoyant gemstone.

English: A cabochon of tiger's eye
English: A cabochon of tiger’s eye (Photo credit: Wikipedia)

In general, for a good cat’s eye effect, you need enough inclusions to make the stone translucent although a faint cat’s eye may occur in mostly transparent material. The inclusion is often rutile, a form of titanium oxide which can also form larger, beautiful golden inclusions in quartz, i.e., rutilated quartz. If the inclusions are oriented on a multi-fold axis, you can get asterism but that’s a subject for another blog post. Interestingly, rutile inclusions can be the cause of a bit of cloudiness to otherwise fine rubies or sapphires. Often heat treatment will cause the rutile to dissolve back into the gemstone, clarifying it and greatly improving its value.

Polished rutilated quartz (Photo credit: Wikipedia)

In hawk’s eye, quartz replaces croidolite fibers (a type of asbestos). In tiger’s eye, the iron in the croidolite has oxidized to a brownish color. In thecommon and quite inexpensive variety, the stones are opaque. However, there is some hawk’s eye and tiger’s eye that is more transparent. In most cat’s gemstones, the stones are translucent, often with a beautiful glow as in the picture above. A very fine cat’s eye is said to “open up” as it is turned in the light. That is, the band is general very sharp but can widen a bit as the stone is turned.

Cymophane is highly prized and can get somewhat expensive, especially above a carat. In addition to body color, the sharpness and centering of the eye effect will determine value. Cat’s eye effects in other gemstones can vary in price depending, as always, on rarity and beauty. In the last few decades, you can also find artificial fiber optic crystals polished as spheres, bears or cabochons. These are very affordable and often are dyed in vibrant colors.

For the fantasy writer, cat’s eyes gems offer another dimension to your ornaments, especially if you describe the way the eye moves across the gem. Maybe in your fantasy novel, when the eye “opens” you actually see a pupil or there is some other magic effect, say a flash of light that illuminates secret letters. And “cymophane” is a word that might add a touch of the exotic to your project.

PS: draft 2 is complete on my current project 🙂 Next up is an outline (ugh) then a ‘quick’ draft 3 before letting readers take a look at it.