4 Toughness of a Gemstone

January 19, 2011By

Usually when gemstones are defined as durable, they include two distinct traits, hardness and toughness.  These terms are not the same and people are often confused between these two.

Cleaving A Diamond

A mineral’s hardness is its ability to resist scratches or abrasions, and hardness is defined on the Moh’s Hardness Scale from 1 to 10, where diamond is the hardest of all mineral with a 10 on the extreme end.  Remember that the Moh’s Hardness Scale is a relative scale and not an absolute scale.

A Chinese Artisan Carving A Jadeite Jade Block

A mineral’s toughness is its ability to resist being fractured. Toughness means resistance to breaking, chipping or cracking — in general, how well a stone holds up under mechanical stress, such as impact from a fall. Toughness rating is usually stated as Exceptional, Excellent, Good, Fair, or Poor.

Even though diamond is the hardest mineral it can chip and fracture in normal day to day wear and tear.  Diamond is formed in the cubic crystal system and has 4 perfect cleavage direction.  A cleavage direction is the weakness plane in the molecular crystal of a diamond.  Hence, an experience diamond cutter will look for the cleavage plane to cleave a big diamond. The toughness rating of diamond is only ‘good’ while that of Hematite is ‘excellent’ while its hardness is only 5.5.

Jadeite Jade and Nephrite Jade have a toughness graded as Exceptional, these two minerals are one of the toughest in the mineral kingdom.  Hence, these minerals can be carved into minute details without fracturing the stone.  Jadeite Jade is composed of micro-crystalline crystals that interlock with each other, making the mineral exceptionally tough.  Nephrite Jade is of a fibrous nature consisting of extremely dense and compact fine-grained fibrous tremolite and actinolite mineral.  Hence, jade can be sawed and carved into very delicate and extremely durable objects of art and adornment.

http://www.gemtec.co.kr, www.gemstoneeducation.com, www.allaboutgemstones.com

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About the Author ()

I am a Graduate Gemologist trained at GIA in New York. I hold an MBA from Cranfield University, United Kingdom and a Bachelor degree in Mathematics. My earlier profession was a banker until I found jade in Myanmar in the early 90s. I have traveled to the fabled Hpakan Jade mines and Mogok in upper Burma with my second son. Three of my children were also Graduate Gemologist, GIA and they are deal in diamonds.

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