Agate - Clear Creek area, Picacho Peak, New Idria District, Diablo Range, San Benito Co., California, USA

So I'm a little confused by this image. It is labeled as chalcedony var agate, however the caption states that it is serpentine with inclusions of other minerals. Which is it?

The caption states it is "agatized serpentine" (serpentine replaced by agate).

"Agatized serpentine" only makes sense if one uses a fairly broad definition of agate ("anything chalcedony").
From what I understand about agates, a direct replacement of serpentine (or any other rock or mineral) by agate would be a mineralogical novelty. Agate proper might have formed in crevices and cavities in a silicified serpentine, of course, and be the reason for calling it "agatized".

I agree with Amir. Given the definition that we are using here on mindat for agate, it doe not seem geologically possible to have agatized sepentine. Thus the description and the placement of the image are needing work.

Chalcedony (var: agate) is certainly the correct classification for this sample. It is probably best described as a becciated agate containing serpentine, silica-carbonate rock and other minerals such as cinnabar, chromite, millerite, etc. where present.

Chalcedony (and agate, jasper and all their varients) are already fairly loosely defined varieties of cryptocrystalline quartz.

Serpentine is just another rock-type. Why do you say that it is not geologically possible to have serpentine that has been agatized?

Karl, how are you suggesting that it should be changed?

Cheers from NorCal, John

"God gave me the stubbornness of a mule and a fairly keen scent." - Einstein

The definition of agate here on Mindat is "a distinctly banded variety of Chalcedony". None of the images of the specimen show any banding at all from what I am seeing.

I would say it "could" be placed in the chalcedony gallery, though it seems a better description of the specimen might be silicified of silica rich serpentine.

So is it a pseudomorph if the chalcedony/agate replaced the serpentine? Or is this a mixture of 2 rock types? Thanks for any clarification...

After reading the cited definition, it seems erroneous to call this an agate on Mindat, but there are numerous other "agates" on Mindat that are not banded either: moss, dendritic, plume, brecciated, fire, etc.

Not sure whether the definition of agate should change or the non-banded "agates" should be changed. Bigger decision than any of us can make.

It does seem that this might be more appropriatel labeled chalcedony without the varietal tag.

Cheers from NorCal, John

"God gave me the stubbornness of a mule and a fairly keen scent." - Einstein

The definition of agate does not need to change or probably better there can be multiple definitions for agate as there are often in a standard dictionary for common words. Agates can be typically banded, but the word is also used to describe other kinds of agate moss, dendritic, plume, brecciated, fire, etc. Eventually I am sure an energetic guy like Amir will add these types to the glossary or chalcedony page with pictures as examples.

Rock Currier
Crystals not pistols.

This material is called plasma agate by the people who collected it locally before the area was closed down. While plasma somewhat fits, being defined here on Mindat as greenish chalcedony, I agree with the others here, agate doesn't. Google plasma agate for many similar images.

OK, I'll change to non-varietal chalcedony. Thanks, Paul.