Saturday, October 2, 2010

October ~ Opal Birthstone

  October is one of several months that have more than one gemstone traditionally associated with them. In this case, I've chosen to feature Opal (which is traditional), and also Pink Tourmaline. 


  The opal with which most people are familiar is Fire Opal. The picture below shows a variety of fine Australian Opal:


Australian Precious Opal


  Opal has several forms: black opal, potch (opaque and has a somewhat waxy appearance), white, and fire (amongst others). Opal has been valued by mankind going back thousands of years; its name derives from the Sanskrit "upala", meaning "precious stone". It was known and valued in ancient Rome, as well as here in America by the Zuni Indians. 


  The lore attached to it tells us that it is thought to increase vitality, to promote enthusiasm and to facilitate insight. One legend tells of a story of the colors of the rainbow being imprisoned in stone by a jealous diety; another attributes its origins to a dragon's eye; another says that it is created when lightening strikes the earth. 


  Opal is hardened silicate gel, and according to one of my trusty resource books, "Rock and Gem", written by Ronald Louis Bonewitz and published by the Smithsonian, we find that 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."

  "But, wait," you suddenly interject. "What about those colors in the precious opal? How are those formed?"


  Well, you are quite right to be a little excited about it! The color play in precious opal is a delight to see. Let's continue, again from the same source:


"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."


  This attribute should also be borne in mind when selecting jewelry with precious opals - the stones that are in bracelets and even rings that may be subject to jarring or heavy wear could fracture or break. 
  
  I noticed that opal fractures conchoidally - if you've ever seen a fracture in glass, you'll notice a series of curves ("like a conch", or shell) in the break. This caused me to hypothesize that perhaps it could be similar to obsidian - it also fractures conchoidally - basically it's a type of volcanic glass. So, opal is actually similar to glass in that it can be fragile.


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 Now we turn our attention to Pink Tourmaline, a lovely stone that appears in many hues - greens, browns, purples and the unique "watermelon" crystal. 



Tourmaline crystals
Faceted Pink Tourmaline in a variety of shades






Sliced Watermelon Tourmaline


  Tourmaline is a relatively common mineral as it is also a member of the silicate family of minerals. "Gemstone quality" is another story altogether! In the U.S., it has been mined in Maine (it is the state gem) and California. Magnificent samples of gemstone crystals have been found in Brazil, Mozambique and Madagascar; other deposits have been found in Russia, Afghanistan, Pakistan, Nigeria and Namibia.

  Again, I turn to "Rock and Gem" for a brief description:

"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."

  The lore of tourmaline tells us that it is known as the "Peace Gem" - promoting calm insight and dispelling fear or negativity. It is thought to promote healing and well-being (on many levels); and is a balancer of the "left" and "right" brain activity, leading to more creativity.





"The gem cannot be polished without friction, 
nor man perfected without trials."  

~ Chinese proverb 



Such are...the Elements of Life...

Please visit my shop at:  http://www.artfire.com/users/GoWestGems 
I have a selection of "Birthday Bracelets" ~ bracelets with Swarovski crystals in the colors of the birthstones.





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