[Jewelry making - Article 00656] - Re: [Orchid] Faceting rough - drilling

[Charles G Heick]

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>        "...would you please post some other numbers for relative
>     hardness of stones using the sclerometer ratings?" 

    Hello Ricco.  With the Mohs' Scale of Minerals being the accepted
    standard among mineralogists and gemologists, there isn't much
    published on Sclerometer values for gem materials other than those
    listed on the Mohs scale.  I do not have access to a Sclerometer
    myself and have only read about it. 

    The relative hardness of minerals found on the Mohs' scale appears
    sufficient for material identification without a need for
    scientifically exact values.  However, I must admit, absolute values
    give us all a better understanding of exactly how hard a material is
    in reference to another.  But, that is the way it is and we aren't in
    a position to change almost two centuries of tradition. 

    In the gem world, relatively speaking, there are very few natural
    gemstone materials harder than 7.5 on the Mohs' scale.  I did a
    search and other than those listed on the scale itself, only found
    twelve rated 7.5 and higher: 

	Andalusite    7.5
	Beryl         7.5
	Euclase       7.5
	Garnet        7.25-7.5
	Hambergite    7.5
	Phenakite     7.5
	Sillimanite   7.5
	Tourmaline    7.5
	Zircon        7.5
	Spinel        8.0
	Taaffeite     8.0
	Chrysoberyl   8.5

>        "If you have information about relative toughness of stones and
>     how that is measured..." 

    A gemstones toughness, along with hardness and stability, determines
    its durability.  Toughness is rated as either exceptional, excellent,
    very good, good, fair or poor.  I do not know what tests are done to
    determine a stones toughness rating.  I have read of the Briggs'
    scale for the ranking of brittle minerals.  Fragments of two
    different materials are positioned on a scale and pressed against
    each other until one of them breaks.  The one that breaks is lower in
    toughness.  Sorry I couldn't be of greater help to you. 

Charles Heick 

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