[Rockhounds] The world's largest crystal cave

Fri Aug 5 18:43:42 PDT 2022

Expanding on "vug," vugs can be simply the hollows formed by "frozen" gas
bubbles in igneous flows.

On Fri, Aug 5, 2022 at 6:40 PM <linda at middleearthminerals.com> wrote:

> Alan, I think that's essentially correct except that I've seen other
> minerals (zeolites, for example) forming the "rind" although of course,
> quartz (including chalcedony and agate) is the most common rind.
> Sometimes,
> especially for sedimentary geodes, the quartz rind is diffuse, permeating
> the sandstone (or other matrix material) strongly enough to take a polish.
> And occasionally the rind is a cast.  The polyhedra from Brazil and
> elsewhere are thought to be quartz pseudomorphing calcite, and they result
> in angular "geodes" which some people may reject as geodes but any
> mathematician would recognize as topologically equivalent!
>
> The mindat definition of geode includes this:
> "Geodes differ from vugs in that geodes can be separated free from any
> matrix, because the walls of geodes are strong enough to maintain the
> integrity of their initial shapes."
>
> To me, that would include what some people might call a vug if the vug is
> encrusted thickly enough everywhere to allow for its intact separation from
> the matrix.  The judges at the San Diego Fair were willing to admit geodes
> with rinds of various minerals as well as those of angular shapes.  Of
> course, they may have been pandering somewhat to the public's taste because
> the broader the definition, the better the display.
>
> Linda
>
> -----Original Message-----
> From: Rockhounds <rockhounds-bounces at rockhounds.drizzle.com> On Behalf Of
> Alan Goldstein
> Sent: Tuesday, July 26, 2022 4:59 PM
> To: Rockhounds at drizzle.com: A mailing list for rock and gem collectors
> <rockhounds at rockhounds.drizzle.com>
> Subject: Re: [Rockhounds] The world's largest crystal cave
>
> I realize that like the word "theory," geode has multiple definitions. I've
> read that - in geological terms - a geode is quartz-lined somewhat
> spherical
> rock within sedimentary or igneous rocks and a "vug" is a hollow pocket
> lines with crystals (no quartz rind). With that in mind, the beautiful
> calcite-lined cavity in Spain is a vug. What have you read about the
> difference between a geode and vug?
>
> Alan G.
> ________________________________
> From: Rockhounds <rockhounds-bounces at rockhounds.drizzle.com> on behalf of
> Kreigh Tomaszewski <kreigh at gmail.com>
> Sent: Monday, July 25, 2022 8:51 AM
> To: Rockhounds at drizzle.com: A mailing list for rock and gem collectors
> <rockhounds at rockhounds.drizzle.com>
> Subject: [Rockhounds] The world's largest crystal cave
>
> In abandoned silver mine in Pulpí, in Spain's south-eastern Almería
> Province, lies a treasure that's not made from any precious metal at all.
> Instead, what's hidden here is the world's largest geode – a natural
> crystal
> phenomenon that has stunned scientists.
>
> As Mila Carretero, geologist and coordinator of the Pulpí Geode, explained,
> a geode is a cavity inside a rock that is covered with crystals. Sitting
> against a backdrop of oversized crystal spars, she broke open a tiny rock
> with tiny gems inside, to show a comparison. "It's the same as the one I
> have behind me, only this one is a super-sized version," she said with a
> laugh as she pointed over her shoulder.
>
> The Pulpí Geode is eight metres wide, two metres high and two metres deep.
> "When it comes to a geode, by definition, this is the biggest ever
> discovery," she noted, adding that Pulpí is not to be confused with another
> crystal marvel, the Naica Mine in Mexico, which has larger spars (15m long
> compared to Pulpí's two metres), but which is a cave lined with crystals
> rather than a geode.
>
> The geode here in Spain was originally spotted by miners in the Mina Rica,
> a
> silver mine which operated from 1873 to 1969. But it wasn't until years
> later, in 1999, that geologists found it again and brought it to the
> world's
> attention.
>
> "When [the original miners] blasted this rock and found a geode, they
> probably got upset because they didn't like finding these crystals," said
> Carretero. "It meant extra work to get rid of them. They weigh a lot and
> were not profitable."
>
> Though scientists are still researching it, they believe the whole area was
> once underwater. At a certain point, volcanic activity fractured
> sedimentary
> rocks and filled them with hot fluids. When the fluids cooled, the crystals
> started forming.
>
>
>
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