About the Book
Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Pages: 28. Chapters: Feldspar, Amblygonite, Turquoise, Kernite, Kyanite, Ulexite, Plagioclase, Bytownite, Labradorite, Wollastonite, Meridianiite, Ajoite, Pyroxferroite, Chalcanthite, Nambulite, Microcline, Kermesite, Rhodonite, Oligoclase, Albite, Gabrielite, Andesine, Hilgardite, Anorthite, Kochite, Fluckite, Astrophyllite, Chaidamuite, Emmonsite, Chloritoid, Amarantite, Lulzacite, Pectolite, Franckeite, Frankamenite, Amesite, Utahite, Okenite, Sassolite, Siderotil, Aenigmatite, Axinite, Pyroxmangite, Alunogen, Baumhauerite, Cylindrite, Gormanite, Zircophyllite, Anorthoclase, Polyhalite, Erebus Crystal, Althupite. Excerpt: Turquoise is an opaque, blue-to-green mineral that is a hydrous phosphate of copper and aluminium, with the chemical formula CuAl6()4(OH)8.4. It is rare and valuable in finer grades and has been prized as a gem and ornamental stone for thousands of years owing to its unique hue. In recent times, turquoise, like most other opaque gems, has been devalued by the introduction of treatments, imitations, and synthetics onto the market. The substance has been known by many names, but the word turquoise, which dates to the 16th century, is derived from an Old French word for "Turkish," because the mineral was first brought to Europe from Turkey, from the mines in historical Khorasan Province of Persia. Pliny referred to the mineral as callais and the Aztecs knew it as chalchihuitl. Even the finest of turquoise is fracturable, reaching a maximum hardness of just under 6, or slightly more than window glass. Characteristically a cryptocrystalline mineral, turquoise almost never forms single crystals and all of its properties are highly variable. Its crystal system is proven to be triclinic via X-ray diffraction testing. With lower hardness comes lower specific gravity (2.60-2.90) and greater porosity: These properties are depe...
