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Mineral Id'ing....., Quartz, Agate, Chalcedony........
CP
post Dec 5 2007, 01:30 PM
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Hey Ya'll!

Thought this would make an interesting topic....... happy.gif

Quartz, agate, chalcedony, jasper, flint, chert, onyx, sardonyx......and the list goes on huh.gif
Many of these are used "loosley" by many of us ........and probably drives geologists/mineralogists absolutely nuts!!!! laugh.gif

They all have some similarities but yet are different.
Well what are the differences? Kind of a broad question minerally speaking but lets see if we can hash some of it out.

Using the other of the 2 best websites on the net Mindat wink.gif biggrin.gif we will first take a look at the Quartz data page.....
Here you will find most anything you wanted to know about quartz including interesting stuff like ......"Quartz is the most common mineral found on the surface of the Earth."

Now....Quartz (hardness 7) also includes chalcedony and agates but is listed seperately so we will check them shortly.
Quartz is typically transparent, translucent with color ranging from colorless, purple, rose, black, yellow, brown, green, orange, etc......and in "Crystallography of Quartz" we find .......
Morphology-Typically long prismatic with steep pyramidal terminations, but may be short prismatic to nearly bipyramidal; fibrous (agate & chalcedony)

Then as you scroll down the quartz data page you will see "varieties of quartz" by name and those include jasper, flint, chert along with the well known amethyst, smokey, citrine, etc.
Cool .. biggrin.gif
On a short side note here we should mention Geodes as well since they often contain quartz crystals.
Also, we should mention the definition of "Enhydro" here as well.......meaning the geode, or crystal contains a water bubble......OOOOOOO Neato! cool.gif

Now we will look at the chalcedony.......Crypto-crystalline varieties of Quartz
Cryptocrystalline is a rock texture which is so finely crystalline, that is, made up of such minute crystals that its crystalline nature is only vaguely revealed even microscopically.

From Mindat's chalcedony data page.....
QUOTE
Traditionally defined as a fibrous cryptocrystalline variety of Quartz, more recently, it has been shown that much Chalcedony is a mixture of Quartz and Moganite, another silica mineral.

When it is concentrically banded (often in rather wild patterns) it is called by the subvariety name Agate. When it is in flat layers/bands it is called by the subvariety name Onyx.

[Note: Many non-banded forms of chalcedony - such as Moss agate - are often erroneously called 'agates'. True agate is concentrically banded. Mottled and included chalcedonies are more properly called simply 'chalcedony.' Petrified wood (agatized wood) is the name given to fossil wood where the replacement of the wood is by chalcedony, but the banding in this case is due to the wood structure - not concentric deposition of the chalcedony - and the material is chalcedony, not true agate.]


Then further down the data page you will find hardness is 7 and a list of "variaties of chalcedony" which include agates, petrified wood, onyx, sardonyx, bloodstone, jasper again and and and ..... smile.gif

So the quartz, agate, chalcedony, jasper, flint, chert etc do have some differences to tell which is which and of course there is much more info on those data pages than I've quoted here.....take some time to check out the Mindat data...it's very cool stuff.
There is just a ton of good info there and I learned a couple things reading all this!
biggrin.gif
Get a fresh cup of coffee.....soda or what ever and enjoy!

Have fun sortin' all the rocks again afterwards too! laugh.gif

CP


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faaus
post Dec 5 2007, 05:32 PM
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That's a mighty interesting topic CP!

There's always more to learn and explore. The good thing is it's fun!

Thanks,
faaus
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Denise
post Dec 10 2007, 09:23 AM
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Great info Dan! smile.gif

Another great way to help you identify is using the
Mohs Scale to test the hardness.

Mohs Scale


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CP
post Dec 15 2007, 11:09 AM
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Cool link for the Id'ing thread Denise......Hardness test help figure out the puzzle.

Here is another bit of info that helps How rocks are classified-USGS
On that page you can learn how Igneous, Sedimentary, and Metamorphic rocks form and the variations in each classification.
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CP
post Mar 3 2010, 01:34 PM
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We thought this might come in handy for everyone too.
This is a link to Geology.com's printable mineral identification chart. Should be a good reference for us all.
Geology.com - Printable mineral identification chart

Happy diggin'! emoticon-misc-004.gif

CP


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Denise
post Jun 21 2012, 04:13 PM
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There is some very helpful information and links in this thread, so I thought I would bring it back.

emoticon-misc-004.gif Keep digging in everyone! Knowledge is power! happy088.gif


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CP
post Jul 23 2015, 12:29 PM
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Been a while since anyone added any links to this thread so I thought I'd bring it back with another useful tid bit....
Another great link to add in on this thread .... several club members use/post this one up around the forums and it's a very simple specific gravity test.
I recently used this SG test to help with verifying some aquamarine pieces for faceting that were not whole crystals and that seems to be exactly what they are.....sweet blue aquamarines signs021.gif

This is a simple test to do with a digital scale and a small dish of water and suspend the specimen with string or paperclip....try it out, it's pretty neat! happy112.gif
Here is a link to the test description posted on John Betts website specific gravity test


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