TURQUOISE BUYING GUIDE*
The always-popular turquoise is enjoying a huge revival in designer jewelry and current fashion. Turquoise is available in a variety of shades of blue and green with varying degrees of matrix. Here is a guide to understanding the types of turquoise available.
Natural turquoise, an aggregate of copper aluminum phosphate hydrate, formed under heat and pressure, is often soft or porous when mined. The various colors found in turquoise result from the presence of either copper or iron -- vivid blue is from copper and the softer green tones from iron. Turquoise stones can also have patterns of brown, yellow ochre and black matrix, produced from copper compounds. True turquoise has an opaque, waxy luster that may or may not include matrix, depending on the type of turquoise.
There are three main stabilization treatments currently applied to turquoise: paraffin polish, polyresin polish and basic stabilization through the impregnation of a colorless bonding agent, commonly plastic, into porous turquoise gemstone beads. This stabilization increases the durability, hardness, chemical resistance and uniform appearance of the turquoise. Stabilization frequently darkens the color of turquoise, giving it a glossy appearance.
TYPES OF TURQUOISE
Sleeping Beauty Turquoise
Sleeping Beauty turquoise, from the Sleeping Beauty mines in Arizona, is the most prized in the world and often exhibits a vivid blue color commonly known as a ''Persian color.'' Many Sleeping Beauty stones are treated with the trademarked Zachery process, in which the soft stone is made denser to stabilize color and reduce porosity.
Stabilized turquoise is widely available and a popular choice for use in jewelry designs. The stone is chemically treated by adding an epoxy resin for increased hardness and enhanced color. With a permanent color and nice matrix, stabilized turquoise is a beautiful value.
Porous white turquoise from China, after it is stabilized and dyed, is often referred to as chalk turquoise. It is generally dyed lively shades of blue, apple green, lime green and fuchsia pink. This form of natural turquoise has a white chalk-like consistency and has the same chemical composition as turquoise with one exception, it does not contain copper, the element that causes the blue color of naturally occurring blue turquoise. Chalk turquoise beads are popular for jewelry because of their hardness and bright colors. Most of the time, chalk turquoise will have a matrix pattern, often resembling subtle crackles.
At Fire Mountain Gems and Beads, if a stone resembles turquoise in appearance, but is not true turquoise, it will appear in quotation marks (''turquoise''). Great examples of this are the varieties of dyed jasper, known in the industry as African ''turquoise,'' that have an exotic blend of green base colors and dark matrix, making it a fine turquoise substitute.
Yellow ''turquoise'' has a subtle blend of gold, greens, browns and black colors of quartz and jasper gemstones that many times will come from the same mines as turquoise. Yellow "turquoise" is wonderful for earthy and fall-themed jewelry.
What is commonly sold and known as white ''turquoise'' is actually a white magnesite. This creamy, white stone has either a brown or black matrix that resembles the patterns found in dry creek beds or crackled antique pottery. It can also be dyed dark shades of turquoise blue and green with stained deep black or brown matrix patterns, and sold as Tibetan "turquoise." This material can also be seen dyed orange, red and other colors.
Howlite and Mountain "Jade"
Affordable turquoise substitutes can also include matrix-free howlite, dyed a stunning turquoise-blue, and bright blue-colored, matrix-free mountain ''jade.'' Howlite is found in continental evaporite deposits and other borate minerals in the form of nodules that resemble cauliflower. The color of turquoise-blue dyed howlite is not permanent, so application of an artists' fixative is recommended to stabilize the color. Turquoise-blue colored mountain "jade" is actually a high-grade dolomite marble mined in Asia and dyed a wide variety of colors including the bright turquoise blue. Both of these stones are an economical way to incorporate the look of turquoise into your jewelry.
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