Those who are born in October have the pleasure of enjoying two birthstones to commemorate their birthdays –tourmalines and opals.
Opals are formed in near-surface volcanic rocks, within cavities and cracks. In sedimentary volcanic ash rock, percolating water in the ground dissolves silica that eventually precipitates to form the opal, sometimes becoming the replacement material for fossils (shells, bones, wood) whose original material had dissolved away.
Opals are notable for their "play of colors" – many stones flash the colors of the rainbow when moved, because of the interference of light on small cracks and other internal structural differences. Additionally opals have characteristic colors because of the impurities within the stone. The milky or pearly appearance of some opals are due to inclusions of small gas bubbles. Yellows and reds prove the presence of iron oxides. The amazing black opals that sometimes flash green, blue and red get their color from magnesium oxides and organic carbon within the stone.
The primary source of opals is Australia, noted for its wonderful black opals. Fire opals were first mined in Mexico, and continue to be produced today. In the U.S, brilliant fire opals are found in Nevada as well. Other commercial sources of opal are Brazil, Honduras, Nicaragua, Guatemala, Japan and Ireland.
The name opal is derived from the Sanskrit word "upala", as well as the Latin "opalus", which means: "precious stone".
The other birthstone for October is the tourmaline - a gemstone that exhibits the broadest spectrum of gemstone colors. Gem-quality forms of this mineral have been misidentified in the past, as rubies, emeralds as well as sapphires. Actually, a legendary tourmaline-the size of a pigeon’s egg-belonging to the Russian Empress Catherine the Great was long thought to be a ruby. The name of this gemstone is believed to derive from the Singhalese (Sri Lankan) word "toramalli", a term used for yellow, green or brown stones, which means "something little out of the earth".
Most tourmalines are found in a myriad of colors: yellow, green, red, blue, pink, brown and black. Some even have bi-colored properties. A valued bi-colored variety of tourmaline, found in Brazil, is called the "watermelon". The outer edges of the gem are green, transitioning to a transparent white zone that gives way to a pink or light red interior.
Also, tourmaline has a noteworthy property: when it is warmed or rubbed, it attracts small bits of paper, lint and ash. The reason this happens is because the gem becomes charged with static electricity. Actually, Benjamin Franklin used this gem in his studies of electricity. Also, maintaining a tourmaline exhibit at museums needs constant cleaning of the gemstone because heat from lights of the display case create a charge in the stone that attracts dust.
Compared with other gemstones, tourmalines are a somewhat quite recent discovery. Among some people though, the stone is known as the "peace stone", known to dispel fear and make its wearer calm.
Which one’s your favorite, opal or tourmaline? Share with us in the comments below.