I had assumed she was just super hard on her jewelry, but even so,
with a hardness of 9.25, you'd think it would be difficult to break
one. From my observations, it seems that although they are hard,
the crystal structure isn't very resistant to cleaving. What say
you gemologists/gem cutters?
Since moissanite does occur naturally as inclusions in diamonds
found in certain iron-nickel meteorites and kimberlite deposits,
gemologists refer to it technically as synthetic moissanite. Some
refer to it by its name as a true chemical compound, Silicon Carbide.
Either way, it is a strange gemstone.
Before diving into the important differences as regarding this
thread, I should explain to the few who don’t understand the
difference between hardness and toughness. Hardness is just that; how
hard the material is. It is usually determined by scratching it with
points of different hardnesses until it scratches. Toughness is a
representation of how easily the material will break, or fracture. My
favorite comparison is diamond vs. jade. Diamond, with a hardness of
10 can abrade any material. You can use it to fashion a hammer out of
jade (hardness of 6 or so). While nowhere near as hard as diamond,
jade is exceptionally tough. A person can take that jade hammer, give
that diamond a good clout on a cleavage direction and break it just
as nice as you please. If you try this at home, bear in mind that, in
reality, it is very difficult to accomplish this feat without
incredible precision. Diamond cleavers (yes, they still exist) are
extremely skilled people who carve a small nick in the rough diamond
and use a sort of wedge with a hammer to accomplish it. We once tried
it with a hammer and anvil and failed miserably.
Okay, back to the thread. Moissanite’s toughness is always listed as
"excellent" because it has no distinct cleavage. Diamond’s toughness
is rated as “good in cleavage directions (there are four),
exceptional in others.” So what this means is that moissanite is a
little tougher in all directions than diamond’s WEAKEST direction and
has a conchoidal fracture, while diamond’s has a step-like fracture.
Diamond’s weakest direction is very difficult to affect when properly
cut, but moissanite’s is available in any direction.
Everyone knows that diamond’s hardness on the mohs scale is 10, the
hardest. What many don’t know is how misleading the mohs scale can
be. In the first nine levels of hardness, it can be said that each
number is more or less twice as hard as the preceding number. That
isn’t precisely true, but it is quite close enough to illustrate. The
last number 10, however, is practically 100 times harder than 9. So,
at 9.25, moissanite is still less than half as hard as diamond.
That’s why your grandmothers’ diamond still has nice, crisp facet
junctions while her sapphire’s is heavily abraded. If she wore
moissanite, it would be just so. That is, if it didn’t break when
smacked on the corner of a table.
So, although fairly hard and tough, it seems to exhibit a brittle
nature. I’ve seen its’ crystal system listed as hexagonal, trigonal
and isometric. Most other gemstones have only one crystal system.
This is what I meant by it being a strange material. Most gemologists
learn how to separate it from diamond which is easy, since it is
doubly refractive with enough birefringence that you can usually see
double facet images through it. But with such a weird crystal
structure, it’s no wonder it doesn’t behave in concert with its’
hardness and toughness.
I’ve never cut any of this material because I’ve never seen any
rough. I don’t think Charles & Colvard allow it to be available to
James S. Duncan, G.G.
James in SoFL