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choosing tools for working jasper/chalcedony/quartz



 
 
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  #11  
Old June 25th 09, 04:31 PM posted to rec.crafts.jewelry
sunrainor
external usenet poster
 
Posts: 10
Default choosing tools for working jasper/chalcedony/quartz

On Jun 25, 12:46=A0pm, Peter W. Rowe
wrote:
On Tue, 23 Jun 2009 10:00:20 -0700, in rec.crafts.jewelry sunrainor

wrote:

And not sure how to do this, but I'd like to be able to tell people
what my stones actually are - from what I read, it's quite difficult
to actually pin down unless you are either an expert of can do some
tests...where does one look for help in this?


If your stones are, indeed (as the thread title suggests) Jaspers, chalce=

donies,
or other quarts based materials, then you may indeed have a hard time pin=

ning
things down to an exact name. =A0The reason is simple. =A0There may not a=

ctually be
an exact name for a specific variety. =A0 All these materials are essenti=

ally
minor variations on the same stuff. =A0 Quartz is a very common mineral. =

=A0When you
get single solid crystals of the stuff, it can be various colors dependin=

g on
what impurities are in it, thus we get purple quartz called amethyst,
orange/yellows called citrine, etc. =A0 That's the simple part. =A0After =

that, it
gets a bit trickier. =A0Quartz also commonly forms not as single large cr=

ystals,
but as a mass of many microscopic crystals, often mixed in with other min=

or
componants which can change the appearance or give it color. =A0When not =

much else
is in it, the color is a milky white, rather transluscent. =A0If that's a=

mass
without structure, we just call it chalcedony, which is sort of a generic=

catch
all catagory rather than a specific type, since that also includes a numb=

er of
varieties that have various colors too. =A0When that chalcedony forms as =

banded
layers, laid down from a water deposit, then we call it agate. =A0Same ma=

terial,
but the name refers to the banded structure. =A0Agates too, come in a wid=

e range
of appearances, some of which get named for that specific appearance or m=

ore
often, the most well known source. =A0Some agates, like moss agate, may n=

ot have
such a strong banded structure, but they still get called agates. =A0 Whe=

n the
impurities get to a large enough layer that the pigmentation they give me=

ans the
rock is no longer transluscent, but rather an opaque colored mass, then i=

t often
gets called jasper. =A0Again, it's the same basic type of material, diffe=

ring in
the amount or color of the impurities. And then the jaspers get named oft=

en for
where they are found, or for prominant aspects of their appearance, or bo=

th. =A0

The key here, is that agates, chalcedonies, and jaspers are all varieties=

of the
same mineral forming in slightly different ways with differing appearance=

s and
structures. =A0So the names given are not organized by a strict mineralog=

ical
system. =A0If you're in an area which is not well known for it's lapidary
materials, then while you may find any sort of nice variety of materials =

these
may not exactly fit into one or another of the nicely accepted names, so =

you may
not be able to get more precise than just "jasper" or "chalcedony" or aga=

te. And
even then, more than a few of these materials are sufficiently mixed with=

other
minerals that even these names may not be precisely accurate.

As you say, an expert in the materials could likely give you a definitive=

nice
sounding name. =A0But would that name always be exactly right, or differe=

nt enough
or more accurate from other names one might also have decided on? =A0Not =

always.
It's a bit of a muddy area, describing a myriad of varieties of different=

looks
to essentially related materials that all fall within the same set of
mineralogical/gemological catagories.

There are a few good books published that can give you some clues. =A0Joh=

n
Sinkankas, quite some years ago, published a fine book on the agates of n=

orth
america. =A0I'm not sure if that's the exact title, but it's close. =A0Ni=

ce
illustrations that would help. =A0After that, catalogs showing gems or la=

pidary
materials for sale will also give you clues as to appropriate names to us=

e.

Of course, not all lapidary materials are actually quartz based. =A0There=

are a
large number of other minerals used for gems as well, and each has it's o=

wn name
or set of names for varieties of that material. =A0Telling these apart so=

metimes
can be done visually, and sometimes needs specific tests. =A0You can find=

a number
of good books out there on the subject of gem identification that can giv=

e you
an idea of how this is done. =A0The classic is Liddicoats "Gem Identifica=

tion",
the GIA published text on the subject used in their gem identification cl=

asses.
But there are quite a number of others too.

Hope that helps.

Peter Rowe


Yes indeed it does - I sort of knew this already but you've described
it more clearly - I know that St. Lucia in my area (north) has
rhyolitic rocks, jasper for sure. It's not well known for lapidary
materials at all, but there's definitely a fair amount of these quartz
based materials.

I'm happy with chalcedony for the translucent off-white-ish ones and
jasper for the yellows and reds. There are some that look like jasper
mixed in with lava - ie the dark parts have lots of bubbles and are
rough - these are much more brittle and I thought I'd call them jasper-
lava. Really I just don't want to claim anything that's not true -
like I read complaints about people calling non-agates, agate.

I believe I will go to the library here and see if there's a rock ID
book and if not, I'll go ahead and get one like the one you
suggested...I do think someday I'd like to do some rockhounding trip
(s) and maybe I'll work with stones that aren't local also.

cheers
Finola
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  #12  
Old June 25th 09, 04:32 PM posted to rec.crafts.jewelry
sunrainor
external usenet poster
 
Posts: 10
Default choosing tools for working jasper/chalcedony/quartz

On Jun 25, 12:28=A0pm, Jim wrote:
On Tue, 23 Jun 2009 10:00:20 -0700, sunrainor
discovered a keyboard and, for our
edification and amusement, submitted

As the machine is an all-in-one, you'd probably get the best deal by
purchsing the whole kit-and-kboodle.

Jim


Ahh, that's true - thanks, and for the Google suggestion - will do

I finally feel like I'm getting somewhere

Finola
  #13  
Old June 25th 09, 04:48 PM posted to rec.crafts.jewelry
Peter W. Rowe[_2_]
external usenet poster
 
Posts: 115
Default choosing tools for working jasper/chalcedony/quartz

On Thu, 25 Jun 2009 08:31:45 -0700, in rec.crafts.jewelry sunrainor
wrote:


Yes indeed it does - I sort of knew this already but you've described
it more clearly - I know that St. Lucia in my area (north) has
rhyolitic rocks, jasper for sure. It's not well known for lapidary
materials at all, but there's definitely a fair amount of these quartz
based materials.


Check these definitions. Last I heard, Rhyolite is an igneous rock. Though
silica rich, it is not jasper, nor related to it. Jasper, like other
chalcedonies, is a sedimentary material. Now, you could have rhyolites with
voids, bubbles, etc, form, which later would have jasper or other chalcedonies
deposit within those cavities. One classic example of that structure is
Mexican opal, which often is found filling holes and bubbles within a
rhyolite... But Jasper itself, is not generally referred to as rhyolitic I
don't think...


I'm happy with chalcedony for the translucent off-white-ish ones and
jasper for the yellows and reds. There are some that look like jasper
mixed in with lava - ie the dark parts have lots of bubbles and are
rough - these are much more brittle and I thought I'd call them jasper-
lava. Really I just don't want to claim anything that's not true -
like I read complaints about people calling non-agates, agate.


Again, I'd wonder just how lava and jasper could mix. This would require a
lava deposit below the water table, with sufficient porosity for mineral rich
solutions to penetrate the lava and deposit jasper within bubbles or voids. If
your material looks like lava has flowed into cracks or seams in the Jasper,
then I seriously doubt it's lava. Rather, it's likely something else that could
also deposit within cracks or fissures in the Jasper, at low temps, perhaps
hydrothermally. Hematite comes to mind...


I believe I will go to the library here and see if there's a rock ID
book and if not, I'll go ahead and get one like the one you
suggested...I do think someday I'd like to do some rockhounding trip
(s) and maybe I'll work with stones that aren't local also.


Beyond the basic gem identification book I suggested, which concentrates more on
classic gems, you may wish to be looking more at mineral guides, and see if you
can find some information on the basic geology of your area. If, for example,
you're in an area which does not have a volcanic origin, then you can be pretty
sure you're not finding lava. But this does not rule out other sorts of igneous
rocks (granite, rhyolite, Basalt, etc)

It might also be worth trying to see if a local high school or college has
anyone teaching geology or mineralogy classes. Those folks might be well
familiar with local geology and materials.

Peter

cheers
Finola

 




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