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Scratch Test for Lapis may not be specific

Posted By: Bill
Posted Date: Jun 06, 2010 (08:53 AM)

Message
John:

Your statement "We have several lepis at home whose hardness can be tested by scratching." confuses me and I hope you would be kind enough to clarify for me.

I wonder what you were trying to say was:

Since your "blue corundum" vase could not be scratched (pass the scratch test), therefore it was not made of lapis but since you could scratch those "lepis" at your home, therefore they would
be made of lapis, is this correct?

However, I must point to you that this may not necessarily be true. While it is correct that blue corundum (or sapphire) has a MOH harndess of 9.0 and could not be scratched (by metal which has a hardness of 5.0), however lapis has a hardness between 5 - 5.5 I once did a study of a large number of lapis carvings (and lapis rocks samples) and found that some lower quality of lapis (the one with white Calcite) could be scratched but the better one (with golden pyrite) could not be scratched. The better one all have hardness of 5.5 which is higher than that of metal and could not be scratched. So unless you have a MOH hardness picks (with different hardness such as 5, 6, 7, 8, 9 and 10), you are not going to be able to test the difference between your blue corundum vase and your lapis pieces at home with a simple scratch test.

You really should test their S.G. because in my study I find that the higher of the quality of the lapis the higher their S.G. will be and vice versa.

In short I do not believe you can just say what your vase was made of without specific testing results.

Hope this will help.

Bill

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