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Citrine and Amethyst--Sister Stones: Two Different Colors of the Same Gemstone!
A Brief Introduction to Quartz
Quartz, the most abundant mineral in the Earth's crust, is composed of silicon and oxygen and develops with either macrocrystalline or cryptocrystalline structures. Macrocrystalline forms, like geodes, for example, have very large crystal structures that are visible to the naked eye and include the most well-known varieties such as rock crystal, smoky quartz, rose quartz, amethyst, and citrine. Cryptocrystalline quartz structures are made up of tiny crystals that are to small too be seen without a very high-powered microscope, and include gemstones such as chalcedony, jasper, and agate.
Quartz, at a 7 on the Mohs scale of hardness (with diamonds at 10), is tougher than many other stones, making it perfect for everyday wear. The beauty and incredible variety of this durable gemstone make it extremely desirable by jewelry designers all over the world. In its purest form, quartz is colorless, but is most highly prized for its purple and golden varieties, known as Amethyst and Citrine.
Amethyst and Citrine
Amethyst is the brilliant purple variety of transparent quartz whose color ranges from pale lilac to a very deep, almost black, purple hue. The presence of minute quantities of chemical impurities such as iron and aluminum is what distinguishes the purple color of amethyst from ordinary clear quartz. When heated at low temperatures, paler amethyst can be transformed to a richer deeper purple.
Amethyst is the recognized birthstone for the month of February. The name of this lovely royal colored stone is derived from the Greek word 'amethystos', meaning 'not drunken'. It has long been believed that amethyst protects its wearer from the intoxicating effects of alcohol.
Citrine, one of November's birthstones, is the yellow variety of transparent quartz, ranging in color from a pale amber to a deep, rich yellow-orange or even 'madeira' golden red. This stone gets its name from the French word 'citron', or lemon, and it has come to be called 'The Merchant's Stone' because of the belief that it brings prosperity to those who carry it.
The only chemical difference between amethyst and citrine is the oxidized state of the iron impurities in the purple stone, which is reduced when heated at high temperatures. Naturally occurring citrine is quite rare, the result of natural heat and pressure applied to amethyst. Most of the citrine in the marketplace is actually amethyst that has been exposed to extreme temperatures (about 450ºC, or 842ºF) and pressure in a controlled environment; and the lower grade amethyst usually responds to this manipulation by yielding the most pleasing colors of citrine as a final product.
Ametrine: A Harmonious Marriage of Amethyst and Citrine
Purple and yellow are complementary colors; opposite each other on the color wheel, they work together in fabulous harmony. The purple of amethyst and yellow of citrine are sometimes found together in a single two-tone gemstone called 'Ametrine', where the properties of both stones are found within the same quartz crystal. This gemstone is actually quite rare, occurring naturally in only one known mine in the world, though the price is just as affordable as either citrine or amethyst alone.
Aside from this single mine in Bolivia, ametrine can be produced in the same way citrine is made from amethyst. Citrine that has been created from heat-treating amethyst can be turned back to its original purple color by bombarding it with beta radiation, which reverses the oxidation state of the iron that caused the color change. To make ametrine, an amethyst gemstone is turned entirely into citrine, then a portion of the stone is exposed to beta radiation to make that section purple again. Alternately, ametrine crystals can be created synthetically in a laboratory by 'growing' crystals of quartz with separate zones of various states of oxidized iron.
Protect Your Quartz Jewelry From Losing its Color
It is the chemical impurities present in quartz which give it an incredible range of beautifully sought after colors, and while clear quartz, or 'rock crystal' is fantastic and beautiful as well, if you have a prized amethyst or citrine, you don't soon want to see it fade to near colorlessness due to lack of care.
Long term exposure to bright light or exposure to high heat can fade the brilliance of any colored quartz, as it breaks down those color-yielding impurities over time. Overheating amethyst while creating citrine will actually drive out all impurities, leaving a colorless quartz. That is to say, aside from not storing your precious gemstones in a high temperature oven, it is a good idea to keep them indoors and away from dressers, tabletops, or windowsills that may get a lot of direct sunlight.
Thanks for reading!
You may also be interested in my article What Makes Turquoise Blue? for a brief history of the stone and some interesting facts about the mineral. You'll find out how to spot turquoise impostors and learn about the myth of white turquoise, and see some great photos of turquoise from different mines to see how mineral composition affects the color of this beautiful stone!
Books and Related Products
In this book two renowned experts share their lifelong passion for geodes and their extensive knowledge of world-class geode deposits as they present the latest theories on the formation and occurrence of these amazing mineral gifts of nature. Visit the geode mines of Northern Mexico and Southern Brazil with Brad Cross.