[Rockhounds] opalite vs. not/digital to view?

[Carol Carter-Wientjes]

Hi again Pete,

Thanks for all of your consideration. Given the fact that it does have some 
heft to it, may make it lean towards more chalcedony or even jasper than 
opalite. It sure is easy to cut and polish without too much effort.

The mystery continues! Carol

----- Original Message ----- 
From: <Pmodreski at aol.com>
To: <rockhounds at lists.drizzle.com>
Sent: Sunday, September 23, 2007 3:05 PM
Subject: Re: [Rockhounds] opalite vs. not/digital to view?


> Carol sent a picture of her specimen to Teri and to myself (forwardable to
> more of you upon request, I'm sure), and I've been contemplating it.
>
> It's a good picture, and a nice looking specimen.  It's a nodule  (split 
> in
> half), palm-of-hand size, and it's a dark maroon-red in the center,  kind 
> of a
> chalky-white toward the outside, slightly banded, with one or two  layers 
> or
> patches of translucent gray.
>
> I guess it's still anyone's guess from the appearance, which material this
> is.  The chalky, porcelain-like, white material does make one think of
> opalite; but some agate or chalcedony can have a white, porcelain-like 
> rind  (from
> weathering, I presume) of material like this--some of which could, in 
> fact, be
> opal for all we usually know about it.  I guess I could comment  that I 
> don't
> think I've ever seen any time of opal (common or otherwise) having  this 
> dull,
> dark red color, whereas it is common in varieties of jasper.
>
> I've been thinking abouit what DOES allow us to distinguish opal from
> chalcedony or jasper.  Aside from properties that one needs technical 
> equipment to
> measure, the differences that are visually or otherwise perceptible  are,
>
> opal has a lower refractive index, which gives it a lesser luster, 
> compared
> to quartz, agate, or jasper.  This would make opal look duller and more 
> like
> cloudy or opaque glass or porcelain.  Quartz has a r.i. of about 1.55; 
> opal
> is about 1.45 (water is 1.33; common glass is about 1.52; obsidian is 
> listed
> as 1.50).
>
> opal is lower in density, which would be noticable in a large enough
> specimen; opal is listed as being 1.9 to 2.2; quartz is 2.65.
>
> opal is slighly lower in hardness, listed as being 5 to 6, instead of  7.
>
> As I tried to say before, it's still hard to describe in words, the
> differences in luster and transparency that one sees in opal compared to 
> quartz.  The
> density difference should be helpful; a piece the size of  yours, Carol,
> ought to feel relatively light for its size, if it is really opal,  as 
> compared to
> any type of quartz which will feel "typical" or  moderatelyu heavy.
>
> Does this help at all?
>
> Pete
>
>
>
>
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