[Jewelry making - Article 00105] - Re: [Orchid] Chatoyant Beryl

[Michael . Hing]

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    	Chatoyant beryl (a.k.a. cat's-eye aquamarine when it is blue-green
    in colour) is not particularly well-known, but it is quite
    sought-after as a collector's item.  In addition, because the name
    "aquamarine" has such good name recognition, I would think that it
    might well appeal to the discerning ordinary consumer as well as the
    collector.  It can be very attractive, although the cat's-eye effect
    isn't as fine as in chrysoberyl. 

>         Also, would anyone know whether heat will make this bluer and
>     what the specs are for heating? 

    	I've never actually heat-treated any myself, but I've read a little
    about the heat-treatment of ordinary aquamarine.  Heating blue-green
    beryls usually results in the green tones fading, leaving the blue
    behind.  I believe that the required temperature range starts at
    about 650 degrees centigrade, although I know that hotter
    temperatures are also used.  N.B. if you overheat beryl it will
    eventually decompose into a type of glass, becoming opaque and
    unattractive in the process. 

    	However, there is a general principle in gemstone treatment that
    says that it is advisable to only heat-treat the cleaner, more
    flawless stones.  If you heat-treat a stone with many inclusions, you
    are more likely to end up with breakages.  Chatoyancy in beryl is
    normally due to many inclusions: fine, parallel growth tubes that run
    along the c-axis of the crystal.  These growth tubes might lead to an
    increased risk of the stone fracturing when you heat it.  However, I
    do know that beryl has a pretty low coefficient of thermal expansion,
    so in theory this might mean that the risk of fracturing is slightly
    lower than for some other gemstones (particularly at the
    comparatively low temperatures required for beryl).  If you do
    decide to heat-treat it, you might want to ensure that the
    temperature rise is slow and gradual, and that the stone is not
    cooled down too quickly afterwards. But you should probably consult
    an expert on gem heating first! 

    	The stone sounds interesting - may I ask where you got it? 

	?8-)
	-Michael.



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