Thursday Thirteen ~ Turquoise

Thirteen Things about Turquoise The name comes from a french word which means stone of Turkey, from where Persian material passed on its way to Europe. Turquoise is one of the world's earliest-used gem materials. Uses: as an ornamental stone for carving and jewelry. The ancient Egyptians sent slave convoys deep into the Arabian Desert to extract fragments of this blue gem from the sedimentary rocks where it occurred as a late-forming secondary mineral. The world-famous Persian turquoise (Persia is now Iran), also formed by weathering and chemical reaction, is still considered by many to be the finest ever mined. Turquoise is a hydrous hydrate of copper, aluminum and phosphorus. The internal atomic arrangement of turquoise is such that iron can substitute for the aluminum, resulting in a color variation. Iron-free material is an intense sky-blue. As iron enters the structure, the color shades toward green. Another color feature in turquoise, which is exceedingly popular in the Southwest, USA is spiderweb turquoise. Spiderwebbing occurs when iron oxide, which can range in color from black to reddish, fills in cracks in turquoise. As supplies of gem-grade turquoise inevitably dwindled--even as mining proceeded--the price of the finest natural turquoise climbed out of sight for most lapidaries. Consequently, it has become necessary to treat lower-grade turquoise so that it can be a usable gem material. The earliest successful treatment method was developed by Colbaugh Processing in the 1950s. Recognizing that it was wasteful to cast aside the lower-grade turquoise, the Colbaughs developed a scientific process for strengthening the softer grades of the gem. The process, called stabilizing, brings out the natural color of the gem, while giving it sufficient hardness and strength to survive lapidary treatment. Hardness is 5 - 6. Other Characteristics: color can change with exposure to skin oils.