This polished 19.25-ct Australian black opal shows the cracks known as “crazing.” © Opal Auctions. Used with permission.

Opal Stone - Natural, Tumbled, Gray, 19.25 ct - International Gem Society

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Opal Stone – Natural, Tumbled, Gray, 19.25 ct

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Opal Stone

This polished 19.25-ct Australian black <a href="https://www.gemsociety.org/article/opal-jewelry-and-gemstone-information/" data-wpel-link="internal">opal</a> shows the cracks known as "crazing." © <a href="https://www.opalauctions.com/auctions/1925ct-polished-black-opal-rub-with-crazing-327256" data-wpel-link="external" target="_blank" rel="external noopener nofollow">Opal Auctions</a>. Used with permission.

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In 2012, Donald Clark retired and passed along stewardship of the IGS to the Rosen family, who were longtime members of IGS. Lisa Rosen runs the day-to-day operation of IGS and  <a href="https://www.ganoksin.com/">The Ganoksin Project, a technical resource website for bench jewelers and jewelry manufacturers</a>.  Lisa strongly believes that IGS must remain a cost-effective, accurate, and comprehensive resource for all those interested in gemology. IGS is our passion, and it is a family business.

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The late Donald Clark, CSM founded the International Gem Society in 1998. Donald started in the gem and jewelry industry in 1976. He received his formal gemology training from the Gemological Institute of America (GIA) and the American Society of Gemcutters (ASG). The letters &#8220;CSM&#8221; after his name stood for Certified Supreme Master Gemcutter, a designation of Wykoff&#8217;s ASG which has often been referred to as the doctorate of gem cutting. The American Society of Gemcutters only had 54 people reach this level. Along with dozens of articles for leading trade magazines, Donald authored the book &#8220;Modern Faceting, the Easy Way.&#8221;

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Gemstone	Opal Stone
Natural or man made	Natural
Origin	Australia
Carat Weight	19.25
Gem State	Tumbled
Color	Gray
Transparency	Translucent
Photo phenomena	Play of Color