Many people confuse the words “hard” and “tough.” In everyday language, we use them the same. However, when you are talking about gems, they take on different meanings.
In gemology, hardness means “the ability to resist scratching.” A diamond will scratch a ruby, therefore it is harder.
In the late 1800′s, a scientist named Dr. Moh came up with a handy comparison chart. He took ten common minerals and arranged them by hardness. Today we know that the difference in hardness between the different levels is not the same. Diamond is about 140 times harder than corundum, which is about 80 times harder than topaz, etc. However, the scale is so useful that we still use it.
Toughness has to do with how well a gem will wear; how much abuse it will take. Some gems are brittle and chip easily. Quartz, at 7 in hardness wears very well. It will take a fair amount of banging, without damage. Zircon is about 7 in hardness, but if you put a zircon in a ring the edges of the facets will wear off in a few years. Sunstone and tanzanite are close in hardness, but they have cleavage planes. If hit just right, they will break in two.
So, what do you do with gems that are not tough enough for everyday wear? First realize that ring stones take much more abuse than gems worn anywhere else on the body. We stick our hands in our pockets and purses, refrigerators, boxes and many other places where a ring can strike something hard.
Earrings, pendants, and brooches do not get nearly as much contact with other things as rings do. So, they are ideal settings for delicate gems. If you really want to put a delicate stone in a ring, you can do this if you reserve it for special occasions and do not wear it every day.
To remember the difference between hard and tough, think of wood and glass. Glass is harder than wood, it will easily scratch it. However, wood is tougher than glass. If you hit the two together, the glass will always break first.