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Re: a simple explaination of agate formation

Posted by: Alfred L. Ostrander

Greg, very precise points. You beat me to several points but I will comment on the general quartz family of which agate has long been accepted as a variety. No need to upset the apple cart there as the different varieties have long been established. We will learn more but a radical overturn of the quartz group is highly unlikely. Simply saying that the presence of various phases in a sample along with some impurities makes it a rock is really an over simplification. By that reasoning any specimen with several minerals forming together and some impurities can be called a rock. So all those beautiful well crystallized specimens in our collections are reduced to being just rocks? There is truth to that statement but not in context.

As to not collecting agates in the tropical rain forests of Brazil, think of the agates of Rio Grande Do Sul, Brazil. Although it is in the southern temperate zone it is humid and sub-tropical and forested. People go collect agates in areas with little or no vegetative cover because they are easier to see. That is all. Except for walking some beaches on Lake Superior. Or collecting amidst the pines at Teepee Canyon, South Dakota. Not desert and great agates can be found.

To Daniel, maybe we as geologists need to be more careful when speaking of geologic time. It runs from billions of years to the present. All geologic processes do not run at the same speed throughout all time. How long does it take to grow a quartz crystal in a lab? That does shed light on what many geologists once thought would take a far far longer amount of time. We do keep learning! I am now in my mid sixties.When I was young I thought someone that old was truly ancient. My thinking has changed: time needs to be kept in perspective.

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