Impurity or Inclusion

[Richard M.]

With such an august group present it may be time to ask a question that''s been on my mind a while. I am wondering precisely what the difference is between an impurity and an inclusion. The question came up on another forum today and brought the old question to mind.

I know that even internal cracks are often referred to as inclusions, incorrectly, I think. It seems to me the term should refer only to objects like crystals, fingerprints, etc. encased or "included" inside the stone (although I suppose a wholly internal crack could be called an inclusion). But what about impurities? Are chromophores like vanadium, chromium, iron, etc. considered "impurities" in allochromatic gems? Take for instance a "pure" grossular garnet, which would be colorless?

And when does an inclusion become a flaw? It seems to me that the terminology in this area is very imprecise and confusing. What am I missing?

Richard M.

 

[mogok]

Hi Richard,

I think that everything depends on the way you look at gems. If for you a gem has to be "pure", meaning only C atoms in perfect order missing atoms and no other substance, then a missing atom become a defect and a nitrogen or a Boron atom replacing a C becomes an impurety. If your idea about you gems is that it should be "clean" then any include crystal become an "impurety" like a peice of durt on a clean wihite bed sheet... Or any feather or fingerprint became a "flaw"...
If something has no positive aspect then it is seen only as negative and decribed negatively.

In ruby, sapphires, and many colored stones the concept of a microscope clean stone does not really apply and there is no real price difference between a VVs1 and a VVs2 ruby... Then in rubies mineral inclusions give to gemologists indications about the nature of the stone, its geologic origin, its possible treatments. So in my opinion they are useful as long as they dont make the stone less beautiful with the naked eye. In my opinion a gem with nice inclusions is even more beautiful than a gem without any "internal world". As a result I dont like words like: "flaws", "impureties", etc...
I prefer to use simply "inclusions".

Regarding to chromophores like vanadium, chromium, iron, you cannot say they are "impureties" as it is due the bem beautiful color is due to their presence. The words "Trace elements" sounds much better to me.

All the best,

 

[Richard M.]

Thanks for the great reply, Vincent, with which I largely agree personally. But my question is really more about language usage in the gem trade. No matter how we individually perceive gems we''ll still encounter those widely-used terms when we go to buy or sell a stone.
Are these terms used incorrectly? Are there better ones or more accurate usage?

Richard M.

 

[mogok]

Hello Richard,
Well I think you can use without any problem "Inclusion", "trace elements" and forget about "flaws" and "Impureties"... I think everybody understand. While studying at GIA I was teach not to say: "semi precious", "crack", "fissures",.. all these words with a negative feeling. I think that when you want to sell or to buy a gem you can survive saying "This stones has 2 inclusions near the girdle" instead of "the stone has 2 flaws near the girdle"... Sounds better if you want to sell the stone and if you want to get a good price on a gem which is not yours, better to be nice with it... and its owner: may be he likes the gem?

All the best,

 

[DiamondExpert]

Well, just off the top of my head

...impurities involve chemical perturbations of the inherent crystal lattice structure of a mineral, usually involving chemical or ionic bonding, which may alter its physico-chemical properties

...inclusions are localized physical disruptions of the normal crystal lattice structure with defined and limited boundaries (visible with the unaided eye or at magnification) and may or may not involve the surface of the stone...inclusions do not involve an alteration of the chemical composition of the mineral.

Flaw is a non-gemological term charged with value judgement, and therefore not very useful.

 

[Cave Keeper]

Perhaps ''impurities'' are more consumer-related lingo.

For example, many Chinese who buy Jadeite jewelry would regard black spots as ''flaws'', ''defects'', ''impurities'', etc. which may even prevent those stones from bringing good luck to the wearer. And the same reasoning probably applies to Hindu wearers of precious stones, especially rubies and emeralds.

 

[DiamondExpert]

I see your point, but not sure I agree entirely...impurity might be thought of nature''s way of doping with an ion/atom not usually present in a crystal which actually changes its chemical properties - e.g., conductivity, color, etc.

 

[Richard M.]

Gary,

I personally agree with your definitions. But in many trade situations I''ve heard references to inclusions as "impurities." In researching the issue I ran across Richard Liddicoat''s definition of the term "imperfection" as "Any surface or internal flaw or inclusion in a gem." He uses both "imperfection" and "flaw" despite implicit value judgments. Words, words, words...

Richard M.

 

[DiamondExpert]

Richard - Interesting, and useful because Liddicoat is at least defining his term, which lessens the ambiguity...I think that that''s important when using words which can be variously interpreted/misunderstood as either "lingo" or as generally defined.

Just so your audience knows where you are coming from goes a long way in communicating.