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Colorado Prospector - Gem and mineral prospecting and mining forums _ Prospectors and Rockhounding Field Work _ Mineral Id'ing.....

Posted by: ColoradoProspector Dec 5 2007, 02:30 PM

Hey Ya'll!

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

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

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 http://www.mindat.org we will first take a look at the http://www.mindat.org/min-3337.html.....
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 ..
On a short side note here we should mention http://www.mindat.org/min-7628.html 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!

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 http://www.mindat.org/min-960.html 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 .....

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!

Get a fresh cup of coffee.....soda or what ever and enjoy!

Have fun sortin' all the rocks again afterwards too!

Posted by: faaus Dec 5 2007, 06:32 PM

That's a mighty interesting topic CP!

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

Thanks,
faaus

Posted by: Mrs.CP Dec 10 2007, 10:23 AM

Great info Dan!

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

http://en.wikipedia.org/wiki/Mohs_scale_of_mineral_hardness

Posted by: ColoradoProspector Dec 15 2007, 12:09 PM

Cool link for the Id'ing thread Denise......Hardness test help figure out the puzzle.

Here is another bit of info that helps http://www2.nature.nps.gov/geology/USGSNPS/rxmin/rockchart.html
On that page you can learn how Igneous, Sedimentary, and Metamorphic rocks form and the variations in each classification.

Posted by: ColoradoProspector Mar 3 2010, 02:34 PM

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.
http://geology.com/minerals/mineral-identification.shtml

Happy diggin'!

CP

Posted by: Mrs.CP Jun 21 2012, 05:13 PM

There is some very helpful information and links in this thread, so I thought I would bring it back.

Keep digging in everyone! Knowledge is power!

Posted by: CP Jul 23 2015, 01:29 PM

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

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!
Here is a link to the test description posted on John Betts website http://www.johnbetts-fineminerals.com/jhbnyc/articles/specific_gravity.htm