[Rockhounds] The world's largest crystal cave

[Kreigh Tomaszewski]

According to MinDat...

Definition of vug
A cavity in a rock, lined with crystals, usually of a different mineral
constitution than the enclosing rock. Adj: vuggy. Etymol: Cornish vooga,
cavern or cavity. Also spelled vugh.


Synonym of: bug hole, vogle, vooga hole

See Also: cavity, vuggy porosity, loch

Compare with: druse, miarolitic cavity, Geode, vesicle, cave


Geode
*Geodes* (Greek γεώδης - ge-ōdēs, "earthlike") are commonly independent
spherical masses of resistant mineral matter that are usually hollow. The
extreme filling of a geode so that it is "solid" is also common. Some
people refer to completely in-filled geodes as nodule
<https://www.mindat.org/glossary/nodule>s, but the two names are not always
consistently used. Geodes differ from "nodules" in that a nodule is a solid
mass of mineral matter, but some nodules may have a tiny void space in
their interiors and the distinction between a geode and a nodule may be
barely discernible if the cavity is miniscule. Geodes differ from vug
<https://www.mindat.org/glossary/vug>s 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. Geodes differ from vugs in
possessing an outer mineral layer which is more resistant to weathering
than the host rock. As such, complete geodes commonly weather out of rock
exposures and accumulate in canyons, talus, rock detritus, etc. Many geode
localities occur is desert areas and are elluvial, not alluvial, meaning
the geodes have not been transported by water.

The most common geodes are dominantly quartz
<https://www.mindat.org/min-3337.html>, but geodes may be composed of other
minerals such as calcite <https://www.mindat.org/min-859.html>, goethite
<https://www.mindat.org/min-1719.html>, etc. Many quartz geodes consist of
concentric layers of several varieties of quartz, such as chalcedony
<https://www.mindat.org/min-960.html>, agate
<https://www.mindat.org/min-51.html>, common opal
<https://www.mindat.org/min-5981.html>, and visibly crystalline quartz. The
order of the kinds of mineral layers varies with the particular history of
the formation of geodes. The interior of geodes may also contain a wide
variety of independently crystallized minerals: calcite, pyrite
<https://www.mindat.org/min-3314.html>, kaolinite
<https://www.mindat.org/min-2156.html>, sphalerite
<https://www.mindat.org/min-3727.html>, millerite
<https://www.mindat.org/min-2711.html>, baryte
<https://www.mindat.org/min-549.html>, dolomite
<https://www.mindat.org/min-1304.html>, smithsonite
<https://www.mindat.org/min-3688.html> and quartz. Geodes have been found
in regions that have basaltic lavas, where they fill voids left by gas
bubbles and in cavities in sedimentary rocks, especially limestones.
Occasionally, geodes may be able to be mined, as in Brazil and Uruguay,
when the enclosing rock is easily separable from the geode structure.

Geodes are often named according to a particular feature or mineral they
exhibit or mention where the particular geodes were found. Common informal
names for geodes include: quartz geodes, amethyst geodes, agate geodes,
enhydro geodes, Oco geodes, Keokuk geodes, coconut geodes, etc. Thunder
eggs may occur as geodes or nodules. See also Thunder Egg
<https://www.mindat.org/min-31316.html>.


Note that the Spanish language cognate "geoda" simply means any
crystal-lined vug, so the English meaning used here is narrower.



On Tue, Jul 26, 2022 at 7:59 PM Alan Goldstein <deepskyspy at outlook.com>
wrote:

> 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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