Everyone collecting or buying gemstones knows that some are not so hard as others. Gemstone’s hardness in gauged through Mohs scale. On Mohs scale gemstones is ranked on a scale of 1 to 10. It’s also a fact that majority of the people don’t know what Mohs scale does really mean. The hardness of the gemstone is mistakenly considered the key of its durability. In this article, I‘ll try to sort out some confusions about the hardness of gemstone.
To gauge the hardness or resistance against scratch of many minerals, German mineralogist Friedrich Mohs developed a scale in 1822 and later this scale was named as Moh’s scale. This scale was based on ten readily available minerals. Moh scale is a position showing scale and you have to put two minerals on comparison to know what mineral is comparatively hard.
On this scale diamond and corundum are rated at ten that prove that they have the ability to scratch all other listed gems: while topaz at nine, quartz at eight, orthoclase at seven, apatite at six, fluorite at 5, calcite at four, gypsum at third, and talc at second .This list shows that topaz has the ability to scratch all these gems that have lower ratings than topaz while it can be scratched by diamond or corundum.
It is worth mentioning that Mohs scale only gives relative measurement as it can’t tell anything about how much harder diamond is than other gemstones like topaz or quartz.
It is not right to judge the durability of the gemstone only through its hardness; just hardness can’t be a proof of some gemstone’s durability. For instance, a perfect cleavage is found in the diamond which means it can be broken with a single waft. The same is the case with topaz which is another very hard gem.
Ruby and sapphire are not as hard as diamond but they have no cleavage and the same quality is found in spinal and quartz. Some other gems like emerald are quite hard but they have internal cleavages that often filled by polishing and oiling. Contrarliy, some gems like jade are not hard enough but still very tough due to their specific crystal structure.
Stability is another thing to measure durability. The tendency of a material to be altered as a reaction of heat, light or chemicals is counted as its stability. Some gemstones like aquamarine and peridot must not be contacted with acids. Similarly some gemstones like kunzite, hiddentie and brownish-yellow topaz fade when they are exposed to the sun for long periods of time. Some gems that surround water like opals have the tendency to become crack and dehydrated.
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