Re: Can a gem stone be melted down into a powder substance?

Samantha, thanks for your question.  There are actually two parts to your 
question; the first is can non-metals like rocks and gem stones be 
melted?  The second part of your question is what happens to materials 
once they melt?  Let's try and answer the second question first.

Metals like gold, silver, and copper are pure metals.  When you heat them 
to a high enough temperature, the metal turns into a liquid.  The shape 
that a liquid takes depends upon the container that is holding the liquid 
and upon surface tension.  Most metals have relatively high surface 
tension.

Surface tension is the force that makes materials want to minimize their 
surface area.  Water has quite a bit of surface tension.  If you put a 
drop of water on wax paper, the water forms a round, spherical shape.  
Likewise, if you melt a small amount of gold, silver, or copper on a 
graphite surface, it will form a round droplet.  So, metals generally do 
not turn into powder spontaneously when you melt them since powder has 
more surface area than one large droplet.

Gem stones and rocks are not pure elements, but instead are compounds of 
several elements.  For example, sapphires are a form of aluminum oxide, 
Al2O3.  At http://www.tairus.com/page3.html you can find chemical 
descriptions for several gem stones.  Most are compounds of aluminum, 
silicon, and oxygen with other metallic impurities that give the gems 
their destinctive color.  The major exception to this is diamond, which 
is a form of relatively pure carbon.

When you heat aluminum oxide compounds to high temperature, most of them 
will melt.  And once they melt, surface tension takes over and the molten 
aluminum oxide forms round drops (depending on what type of surface it is 
resting on).  So, most gems will melt but do not necessarily turn into 
powder.

Some materials, however, contain compounds or molecules that break down 
when you heat them, including some aluminum oxide compounds.  For 
example, limestone (marble) is calcium carbonate.  When you heat it to 
high temperature, the elements that make up limestone break down, 
releasing carbon dioxide and water.  An opal is a form of silicon dioxide 
containing quite a bit of water.  If you heat an opal, you also drive off 
the water.  In both cases, you end up with a powder, not because of the 
heat or melting, but because you have produced a chemical breakdown.  And 
when chemical bonds break, they often produce a powdery material, since 
the chemical bonds which held everything in a solid shape have been 
broken.

So, many gems and rocks can be melted, turning into liquids at high 
temperature.  Other gems and rocks will undergo chemical change when 
subjected to high temperature, changing into some other material and 
often turning into a powder as a result.

Then there are a few odd balls, like diamond.  The chemical bonds within 
a diamond are so strong that diamond never actually melts; it turns 
directly into a gas at very high temperature (kind of like dry ice 
behaves).  

One last thing to keep in mind.  The reason that gems are attractive is 
that they are usually single crystals of material.  It is much easier to 
melt a single crystal than it is to form a single crystal from molten 
material.  You might look up things like "gem synthesis" to get an idea 
of some of the companies and techniques that are used to make gem stones.

Thanks for your question.  I hope my answer helps.