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Re: a simple explaination of agate formation

Posted by: Gregg Little

Being of similar "vintage" and speaking of long duration processes, I remember a pre-eminent researcher speaking at my university on a recently accepted theory called continental drift. Long time ago for me, a nano blink of geological time.

Getting back to crystal formation, one of our recent threads was about inclusions and described growing small centimetre-size quartz crystals in a lab over 4 months using seed crystals. I imagine geological processes can match or exceed that given the right conditions. Part of the many variables would include favorable and stable fluid chemistry, high volume, constant temperature and pressure for the duration, etc, etc.

One thing to keep in mind too is that crystals can go through growth phases (ie phantoms) so that further complicates bracketing the time for formation. We humans seem to be time obsessed but the more important question geology asks is, what are the specifics that lead to crystal formation. Time usually is expressed in dating the preceding, concurrent and following processes around the time of crystal formation conditions. These time brackets are usually in the thousands to millions of years and don't necessarily describe when that particular crystal in your hand began and completed its growth.

One of the interesting time frames relates to diamond. It probably takes millenniums to eons for them to form, 10's of miles below the surface, but some of the literature describes their emplacement in kimberlite pipes to be in as little a period as days.

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