[Rockhounds] Life Helps Make Almost Half of All Minerals on Earth

[linda at middleearthminerals.com]

Herwig, that is probably the best definition of a geode that I have ever seen!  Thank you!  I should have thought to look at Mindat.  It included everything that I hinted at.  About the only thing I might add is that the sedimentary geodes often seem to have formed around fossilized remains (thereby coming full circle back to the title of this string, "Life", hooray!) that may in fact be how there came to be "cavities in sedimentary rocks, especially limestones" as opposed to the gas bubbles that leave places for igneous geodes to form.  And actually, to be a bit picky, the "thunderegg" subcategory of igneous geode seems to get its vacant space from cracks formed as the geode substrate solidifies, and the geode substrate itself needs no additional space since it is conjured out of the lava/ashflow, perhaps hardened by cristobalite.  Technically, a gas is indeed being released into the thunderegg cracks, but it's not in the same way or at the same high pressures as the gas bubbles that hollow out those magnificent Brazilian geodes. - Linda-the-geode-lover

-----Original Message-----
From: Rockhounds <rockhounds-bounces at rockhounds.drizzle.com> On Behalf Of Herwig Pelckmans
Sent: Saturday, July 2, 2022 1:42 PM
To: Rockhounds at drizzle.com: A mailing list for rock and gem collectors <rockhounds at rockhounds.drizzle.com>
Subject: Re: [Rockhounds] Life Helps Make Almost Half of All Minerals on Earth

Hi Linda,
I think the Mindat description for a geode is pretty good:
https://www.mindat.org/glossary/geode
Cheers, herwig

Op za 2 jul. 2022 om 20:03 schreef <linda at middleearthminerals.com>:

> This is totally consistent with many (possibly most?) geological 
> definitions since they incorporate the formation process.  For 
> example, a cirque is formed by the head of a glacier.  If it looks 
> similar to a cirque but was not formed by a glacier, then it isn't truly a cirque.
>
> To bring it down to our interests, I believe even the humble geode 
> requires a definition acknowledging formation.  If you don't consider 
> formation, how do you exclude carved vugs, for example?  In my 
> opinion, a geode can be exposed by carving if it could eventually have 
> weathered out as an intact, roughly spherical unit.  This requires 
> that it have some internal structure (often layers of quartz or agate) that produces a "rind"
> tough enough to keep it together while weathering out.  Geodes can 
> form in both sedimentary and igneous environments.  (I even have one 
> that may be
> metamorphic.)
>
> Why define a geode?  I used to exhibit at a county fair and had to 
> guess at what the judges would consider a geode to be.  It turned out 
> to be an intriguing and difficult definition.
>
> -----Original Message-----
> From: Rockhounds <rockhounds-bounces at rockhounds.drizzle.com> On Behalf 
> Of Kreigh Tomaszewski
> Sent: Saturday, July 2, 2022 6:13 AM
> To: Rockhounds at drizzle.com: A mailing list for rock and gem collectors 
> < rockhounds at rockhounds.drizzle.com>
> Subject: [Rockhounds] Life Helps Make Almost Half of All Minerals on 
> Earth
>
> The impact of Earth’s geology on life is easy to see, with organisms 
> adapting to environments as different as deserts, mountains, forests 
> and oceans. The full impact of life on geology, however, can be easy to miss.
>
> A comprehensive new survey of our planet’s minerals now corrects that 
> omission. Among its findings is evidence that about half of all 
> mineral diversity is the direct or indirect result of living things 
> and their byproducts. It’s a discovery that could provide valuable 
> insights to scientists piecing together Earth’s complex geological 
> history — and also to those searching for evidence of life beyond this world.
>
> In a pair of papers published today in American Mineralogist, 
> researchers Robert Hazen, Shaunna Morrison and their collaborators 
> outline a new taxonomic system for classifying minerals, one that 
> places importance on precisely how minerals form, not just how they 
> look. In so doing, their system acknowledges how Earth’s geological 
> development and the evolution of life influence each other.
>
> Their new taxonomy, based on an algorithmic analysis of thousands of 
> scientific papers, recognizes more than 10,500 different types of minerals.
> That’s almost twice as many as the roughly 5,800 mineral “species” in 
> the classic taxonomy of the International Mineralogical Association, 
> which focuses strictly on a mineral’s crystalline structure and chemical makeup.
>
> “That’s the classification system that’s been used for over 200 years, 
> and the one that I grew up with and learned and studied and bought 
> into,” said Hazen, a mineralogist at the Carnegie Institution for 
> Science in Washington, D.C. To him, its fixation on mineral structure 
> alone has long seemed like a monumental shortcoming.
>
>
> https://www.quantamagazine.org/life-helps-make-almost-half-of-all-mine
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