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Quartz is one of the most common minerals on the planet, providing everything from the sparkle in granite to the ticking of wristwatches—the stone’s vibrations are regular enough to keep time. Rock crystal quartz is colorless, but amethyst is...
Quartz is one of the most common minerals on the planet, providing everything from the sparkle in granite to the ticking of wristwatches—the stone’s vibrations are regular enough to keep time. Rock crystal quartz is colorless, but amethyst is purple, citrine is yellow, and aventurine is green. All are varieties of gem-quality, single-crystal quartz. Gem-quality cryptocrystalline (also called microcrystalline) quartz is also called chalcedony, examples of which include agate, onyx, and carnelian.
Because of its ubiquity, evidence of quartz jewelry has been found dating back 7,000 years. One especially ancient find, discovered in present-day Iraq, takes the form of rose quartz beads, making quartz one of the earliest materials used in ornamental jewelry.
Amethyst gets its purple-to-violet color from traces of iron mixed into the “pure” quartz recipe of one silicon atom for every two of oxygen atoms. Amethysts are dichroic, which means they appear bluer when viewed from one direction and redder when viewed from another. Jewelers give amethysts mixed and step cuts, making them perfect for sparkling rings. The best amethysts are mined in the Ural Mountains of Russia, which are redder than Canadian amethysts, which are more violet.
The yellow variety of quartz is called citrine, and also gets its hue from iron, although obviously in different amounts and under different conditions than the iron that turns amethysts purple—heat-treating amethysts will turn those gems a very desirable lemon yellow. Sometimes misnamed as topaz, citrine is often given brilliant and pendaloque cuts.
Aventurine, which ranges from green to brassy, gets its color from green fuchsite mica, pyrite, hematite, and even copper. Because it is opaque, it is usually polished into cabochons or carved into cameos. In some cases, the greens are rich enough to cause confusion with jade.
Of the chalcedony varieties of quartz, agate is perhaps the most diverse. Frequently cut and polished into cabochons, agates come in numerous colors and feature a range of inclusions. Best known are the banded agates, which get their colors from iron and manganese—banded agates are often carved into cameos to reveal their multicolored layers. Moss agates get their green color naturally from chlorite, while black onyx is the result of soaking agates in a sugar solution before boiling them in sulfuric acid, which turns the sugar residues within the porous stone black.
A final class of this widely variant mineral is known as chatoyant quartz, in which fibrous inclusions of crocidolite (also called blue asbestos) produce quartz cat’s-eyes. Add iron oxide to the mix, and the result is a tiger’s-eye. Highly polished cabochons and beads, which have a silky surface, show quartz cat’s- and tiger’s-eyes to their best advantage. In the case of cabochons, the stone is cut so that its interior fibers run parallel to its base.
While quartz itself is not a birthstone, amethyst is the birthstone for those born in February and citrine is one of two gemstones for people born in the month of November (topaz is the other).
Continue readingQuartz is one of the most common minerals on the planet, providing everything from the sparkle in granite to the ticking of wristwatches—the stone’s vibrations are regular enough to keep time. Rock crystal quartz is colorless, but amethyst is purple, citrine is yellow, and aventurine is green. All are varieties of gem-quality, single-crystal quartz. Gem-quality cryptocrystalline (also called microcrystalline) quartz is also called chalcedony, examples of which include agate, onyx, and carnelian.
Because of its ubiquity, evidence of quartz jewelry has been found dating back 7,000 years. One especially ancient find, discovered in present-day Iraq, takes the form of rose quartz beads, making quartz one of the earliest materials used in ornamental jewelry.
Amethyst gets its purple-to-violet color from traces of iron mixed into the “pure” quartz recipe of one silicon atom for every two of oxygen atoms. Amethysts are dichroic, which means they appear bluer when viewed from one direction and redder when viewed from another. Jewelers give amethysts mixed and step cuts, making them perfect for sparkling rings. The best amethysts are mined in the Ural Mountains of Russia, which are redder than Canadian amethysts, which are more violet.
The yellow variety of quartz is called citrine, and also gets its hue from iron, although obviously in different amounts and under different conditions than the iron that turns amethysts purple—heat-treating amethysts will turn those gems a very desirable lemon yellow. Sometimes misnamed as topaz, citrine is often given brilliant and pendaloque cuts.
Aventurine, which ranges from green to brassy, gets its color from green fuchsite mica, pyrite, hematite, and even copper. Because it is opaque, it is usually polished into cabochons or carved into cameos. In some cases, the greens are rich enough to cause confusion with jade.
Of the chalcedony varieties of quartz, agate is perhaps the most diverse. Frequently cut and polished...
Quartz is one of the most common minerals on the planet, providing everything from the sparkle in granite to the ticking of wristwatches—the stone’s vibrations are regular enough to keep time. Rock crystal quartz is colorless, but amethyst is purple, citrine is yellow, and aventurine is green. All are varieties of gem-quality, single-crystal quartz. Gem-quality cryptocrystalline (also called microcrystalline) quartz is also called chalcedony, examples of which include agate, onyx, and carnelian.
Because of its ubiquity, evidence of quartz jewelry has been found dating back 7,000 years. One especially ancient find, discovered in present-day Iraq, takes the form of rose quartz beads, making quartz one of the earliest materials used in ornamental jewelry.
Amethyst gets its purple-to-violet color from traces of iron mixed into the “pure” quartz recipe of one silicon atom for every two of oxygen atoms. Amethysts are dichroic, which means they appear bluer when viewed from one direction and redder when viewed from another. Jewelers give amethysts mixed and step cuts, making them perfect for sparkling rings. The best amethysts are mined in the Ural Mountains of Russia, which are redder than Canadian amethysts, which are more violet.
The yellow variety of quartz is called citrine, and also gets its hue from iron, although obviously in different amounts and under different conditions than the iron that turns amethysts purple—heat-treating amethysts will turn those gems a very desirable lemon yellow. Sometimes misnamed as topaz, citrine is often given brilliant and pendaloque cuts.
Aventurine, which ranges from green to brassy, gets its color from green fuchsite mica, pyrite, hematite, and even copper. Because it is opaque, it is usually polished into cabochons or carved into cameos. In some cases, the greens are rich enough to cause confusion with jade.
Of the chalcedony varieties of quartz, agate is perhaps the most diverse. Frequently cut and polished into cabochons, agates come in numerous colors and feature a range of inclusions. Best known are the banded agates, which get their colors from iron and manganese—banded agates are often carved into cameos to reveal their multicolored layers. Moss agates get their green color naturally from chlorite, while black onyx is the result of soaking agates in a sugar solution before boiling them in sulfuric acid, which turns the sugar residues within the porous stone black.
A final class of this widely variant mineral is known as chatoyant quartz, in which fibrous inclusions of crocidolite (also called blue asbestos) produce quartz cat’s-eyes. Add iron oxide to the mix, and the result is a tiger’s-eye. Highly polished cabochons and beads, which have a silky surface, show quartz cat’s- and tiger’s-eyes to their best advantage. In the case of cabochons, the stone is cut so that its interior fibers run parallel to its base.
While quartz itself is not a birthstone, amethyst is the birthstone for those born in February and citrine is one of two gemstones for people born in the month of November (topaz is the other).
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