Gemstones Q through Z

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Quartz: A family of minerals composed of silicon dioxide. There are two varieties: macro crystalline (crystals visible with the naked eye) and micro (or crypto) crystalline (crystals which cannot be seen without magnification.)
The macro crystalline quartzes include citrine, amethyst, aventurine, tiger eye, and rose quartz, smoky quartz, rutilated, snowy and crystal (also called rock crystal) quartz. The cryptocrystalline quartzes are termed chalcedony. (Also commonly marketed as "quartz" is a series of manmade forms of glass - these include cherry, blueberry, pineapple, and blue "quartz", as well as opalite.)
Hardness: 7
Care: Generally very hardy and trouble free - colored varieties may alter in hue and intensity with exposure to intense heat or light.

Ruby: The ruby is the red variety of corundum (all other colors are designated sapphire). Naturally, there is some variation in just where the line between a pink sapphire and a light-hued ruby is drawn, nevertheless, the distinction is purely semantic, albeit perhaps an attempt to alter the perceived value of the stone.
Treatments: Rubies are commonly colour-enhanced.
Hardness: 9
Care: Like sapphires, rubies are very hardy and safe for normal gemstone care methods.

Sapphire: the non-red variety of corundum (red being ruby), an aluminum oxide mineral. It occurs in a wide range of colors; however, convention dictates that only blue sapphires are simply titled "sapphire", while any other color is included in the name (eg. padparadscha sapphire, white sapphire). Pink is supposed to be classified as ruby, but in practice is often designated as sapphire. Sapphire is the most precious of the blue gemstones, due to its hardness, durability and luster, with translucent cornflower blue being the most desirable hue. Padparadscha, a vibrant orange pink, is considered to be the most precious of the non-blue shades, although there is some disagreement on exactly which shades ought to be given the designation.
Treatments: Sapphires are routinely heated to improve their color, an industry accepted practice.
Hardness: 9
Care: Sapphires are very hardy and safe for normal gemstone care methods.

Some Common Terms:
Umba sapphire - mined along the Umba river in Tanzania. Color range includes blues, purples, gold, orange and pink shades. Lovely pastel shades are typical.
Songea sapphire - from Africa - color range includes deep red rubies, blues, blue greens, greens, yellows, pinks, and \ alexandrite-type (blue in sunlight and fluorescent light, lavender to purple in incandescent).
Tunduru sapphire - from Africa - full color range
Star sapphire - these have fine needle like inclusions which render the stone opaque, and when oriented properly, reflect light to form a moving star. Cut as cabochons to optimize the effect.

Serpentine: is a group of minerals composed of hydrated magnesium silicate. Because it is usually some shade of green, it is often called "jade" (aka Afghan Jade, Green Jade, Lemon Jade, New Jade, Olive Jade, Yellow Jade).
Russian serpentine is a dark mottled form mined in the Ural mountains.
Hardness: varies from 2.5 to 4 due to the varying composition.
Care: safest bet is gentle polishing with a soft cloth.

Smoky Quartz: This lovely brownish-black variety of quartz occurs naturally, but is also commonly created by irradiating or heat treating clear quartz. Hue ranges from blackish "smoky" to golden brown (sometimes named as a variety of citrine). It is a popular gem for unusual faceted cuts and is the national gem of Scotland.
See the entry for Quartz for further information on care and durability.

Sodalite: An intensely dark blue stone with white and occasionally yellow streaks. Mineral identity: sodium aluminum silicate chloride. Often confused with lapis lazuli, which contains sulfur, rather than chlorine.
Hardness: 5.5-6
Care: Clean with warm, soapy water. Avoid steam and ultrasonic cleaning.

Turquoise: A hydrated aluminum copper phosphate, often containing iron. There are many forms of genuine turquoise, as well as numerous imitations. The color encompasses the entire spectrum from blue to green, with various amounts and patterning of black or brown matrix. Turquoise is a soft stone and specimens which are hard enough to be usable in their natural state are rare. The form which I refer to simply as turquoise is stabilized.
Hardness: 5-6
Terms in common usage include:
Natural turquoise - technically should refer only to the highest grade which is hard enough to be used in un-enhanced form - it will absorb body oils and turn green over time. Vendors often call any non-imitation form of turquoise "natural".
Sleeping Beauty turquoise - a popular high grade form with a brilliant blue color and little or no matrix, from the Sleeping Beauty mine in Arizona. Because of it's desirability, pretenders abound and the term is much abused.
Stabilized turquoise - The most commonly available form - impregnated with resin which serves to harden the stone and deepen the color (much as rocks appear darker when wet). Chinese forms may also include wax and/or dye enhancement. Even stabilized turquoise will absorb body oils and darken over time.
Mexican turquoise - mined in Mexico, unique in that it occurs naturally as free-form nuggets. Stabilized.
Mojave turquoise - chunks of turquoise compressed into a block with plastic resin filler and dyed green. A similar product in purple is being marketed as "purple Sleeping Beauty turquoise".
African "turquoise" - actually a blue green jasper mined in Africa
Chalk "turquoise" - a pale stone (often not turquoise) which has been dyed - commonly brilliant blue or lime green.
Howlite "turquoise" - a pale, black-veined stone commonly dyed to simulate turquoise.
Reconstituted "turquoise" - implied to be ground up turquoise assembled with plastic resin - reliable sources suggest that it is generally, in fact, entirely plastic. I don't use this form.
Care: Avoid scratches and sharp blows, as well as hot water and household chemicals.

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