difference in flint & agate?

[mamabear]

I have some flint from WYO, & S.D. I also have a lot of agate. The flint I have looks a lot like agate, especially moss agate. So my understanding is flint is sedimentary & agate is metamorphic. Is this correct? It's hard for me to fathom 2 rocks that look so much a like have such different origins. Is there a common mineral composite that makes them appear so alike?

 

[EricTheCat]

Good eye. Your observation about the similarity between agate and flint is no coincidence. Flint and agate are both sedimentary and both are forms of microcrystalline quartz.

 

[Eu_citzen]

Agate shows concentric banding. Flint doesn't. Both are members of the chalcedony family.

 

[gunsil]

Agate shows concentric banding. Flint doesn't. Both are members of the chalcedony family.

Not all agate, by any means shows banding, and there is flint from Poland that does have very interesting striped patterns in it. They are both chalcedony as you state.

 

[mamabear]

thanks everyone. I thought I had read one is sedimentary & one is metamorphic

 

[mamabear]

just read in my Audubon rocks & minerals, " Chalcedony( also agate) is formed in several environments, generally near the surface of the earth where temps & pressures are relatively low. It commonly forms in the zone of alteration of lode and massive hydrothermal replacement deposit and as bodies of chert in chemical sedimentary rocks. So the info I looked up on line was wrong. I should have listened to Abe Lincoln, "not everything you read on the internet is true."

 

[mamabear]

so metamorphic is made deeper therefore morphed by heat & pressure?

 

[Eu_citzen]

Not all agate, by any means shows banding, and there is flint from Poland that does have very interesting striped patterns in it. They are both chalcedony as you state.

Agate:
Agate: Agate mineral information and data.
Chalcedony:
Chalcedony: Chalcedony mineral information and data.

Quote from the above link:

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.

And, furthermore:

[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.]

There you have it.

 

[mamabear]

thank you EU. I have so many questions & every time I go "rockin" I come up with more. Really try to use my books as much as possible. but usually leads to more questions. Should have been professional student. I would take classes til the very end.

 

[Turkısh Man]

Flint may be too large than the agate,