The Crime of "Falling Skies"
Discussion of the science and lore of rocks, minerals and gemstones, and the roles that they play in our lives. It also may include discussions that are philosophical or spiritual in nature.
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| Photo courtesy of Abhinaba Basu . No endorsement of blog or website is implied. |
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| Garnet Beads |
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| Tsavorite Garnet Crystal {All photos courtesy of: http://skywalker.cochise.edu/wellerr/VGM/intro.htm} |
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| Faceted Citrine with Amethyst |
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| Australian Precious Opal |
"...is deposited at low temperatures from silica-bearing, circulating waters. It is found as nodules, stalactitic masses, veinlets and encrustations in most kinds of rocks. It is especially abundant in areas of hot-spring activity and, as the siliceous skeletons of diatoms, radiolarians and sponges, opal constitutes important parts of many sedimentary accumulations such as diatomaceous earth. It is commonly found as fossilized wood where it preserves the wood's external appearance and cellular structure. Fossil bones and seashells have been discovered in Australia replaced by precious opal, and it also forms pseudomorphs after gypsum, calcite, feldspars, and other minerals."
"Precious opals can form only in undisturbed space within another rock that is capable of holding a clean solution of silica from which water is slowly removed over a long period--perhaps thousands of years. The silica spheres slowly settle out of solution and arrange themselves into an orderly three-dimensional formation...[the] color play...is caused by the diffraction of light through the spheres; opal is, in effect, a diffraction grating...All precious opal is probably relatively young in geological terms, since precious opal cannot withstand the heat and pressure of burial and metamorphism."
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| Tourmaline crystals |
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| Faceted Pink Tourmaline in a variety of shades |
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| Sliced Watermelon Tourmaline |
"Crystals of tourmaline are generally prismatic. Colored crystals are very strongly dichroic, and frequently display color zoning. Tourmaline is abundant, and its best-formed crystals are usually found in pegmatites and in metamorphosed limestones in contact with granitic magmas. Tourmaline minerals are resistant to weathering, so they accumulate in gravel deposits -- the origin of its name is the Singhalese word "turamali", meaning "gem pebbles". For the same reason tourmaline is an accessory mineral in some sedimentary rocks. Gem-quality tourmaline occurs in numerous localities. Tourmaline's piezoelectric properties mean that it is also an important industrial mineral. It is employed in pressure devices such as depth-sounding equipment and other apparatus that detect and measure variations in pressure. It is also used in optical devices for polarizing light."