Gems, color

Out of the mouth of the six-legged triangle spill a number of tiny gems colored translucent emerald or sapphire. The gems undulate, sprout legs, and scurry away into the distance. 

Nitride Homogeneity range 1 — x at 1700 K Structure (Bravais lattice) Lattice parameter (room temp.) (nm) Density (gem ) Color Microhardness (room temp.) (GPa) Melting point (K) Heat conduct. (room temp.) (Wm- K- ) Thermal exp. coefficient at 1000K(10 K- ) comp. (1 — x) Electr. resistance (room temp.) ( xl2 cm) Supercond. transition temp. Tc (K) comp. (1 — x)... 

NMR spectroscopy is a convenient method for structural study of the equilibrium between the colored and the colorless form of spirobenzopyran. In the H-NMR spectra, the chemical shifts of gem methyl groups in 3 -position, (V-methyl group,2,11 and methine protons in 3- and 4-position are important to distinguish between the colored and colorless forms. 

Colored beryl gems, for example, aquamarine, are highly sought-after... 

Black Opal With Brilliant Vivid Colors. Smithsonian Gem and Mineral Collection,... 

Throughout history civilization has treasured the rarity and beauty of fancy colored diamonds. The stunning diamond from India known as the Hope Diamond, once a part of many royal inventories, is now the premier attraction of the Smithsonian Institution (see color Fig. 4.3.1). While the size of the diamond at 45.52 carats has certainly contributed to the public s interest in the gem, the intense blue-violet color of the stone is generally considered to be its most captivating feature. First described in the mid 1600s by the French merchant traveller Jean Baptiste Tavernier as un beau violet (a beautiful violet), the gem also acquired the title Blue Diamond of the Crown or the Royal French Blue when in possession of King Louis XIV of France. The blue color is attributed to trace amounts of boron in the carbon matrix of the stone. Substitution of carbon atoms by nitrogen leads to yellow diamonds, such as the famous canary yellow 128.51-carat Tiffany diamond. 

Gems and Precious Stones Color in Minerals. Jill Banfield, The Department of Geology and Geophysics, University of Wisconsin-Madison, http //www.geology.wisc.edu/ jill/Lect7.html... 

Chemical treatments are commonly applied to imperfect gems to improve appearance and/or enhance the color. Although gem treatment is legal, dealers must disclose whether or not a specific specimen has been treated and what treatment has been applied. As treatment technology improves, the gem industry is increasingly aware of and sensitive to the presence of both disclosed and undisclosed treated gems in the marketplace. Thus, there is a need to be able to reliably detect chemically treated gems with a minimally-destructive technique. 

Another very well known fibrous variety of silica is the gem called opal. Opal is actually a hydrated form of cristobalite whose fiery primary colors come from the diffraction of light by aligned water and siliea fibers. Lus-... 

Quartz is found in several forms in all three major kinds of rocks—igneous, metamorphic, and sedimentary. It is one of the hardest minerals known. Geologist often divides quartz into two main groupings—course crystalline and cryptocrystalline quartz. Course crystalline quartz includes six-sided quartz crystals and massive granular clumps. Some colored varieties of coarse crystalline quartz crystals, amethyst and citrine, are cut into gem stones. 

Hard metal that is white in pure state but brilliantly colored as compounds in trace amounts it gives gems their colors used in paints, automobile bumpers, and stainless steel. 

The red color of the ruby is also caused by the presence in it of a trace of chromic oxide, which distinguishes this costly gem from common crystalline corundum (alumina). Thus chromic oxide, according to F. H. Pough, is the most valuable commodity in the world when purchased in the form of a ruby (84). A beautifully illustrated article on synthetic rubies appeared in the Journal of Chemical Education for June, 1931 (85). 

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