FMF - Friends of Minerals Forum, discussion and message board

[Enrique Llorens]

Quartz from Peru

[Michael Shaw]

This tiny little Quartz var. Herkimer diamond has always been one of my favorites because of the clarity and unusual morphology. I collected this one back in 1962.

[geofossile]

Quartz with Muscovite (variety fuchsite) from Itremo, Madagascar.

[Jordi Fabre]

[Bergur_E_Sigurdarson]

My favourite quartz, with paralell secondary growths.

Main crystal : H 85mm x W 27mm x D 25mm

Bought in the village of Muzo from local vendor.

(Can anyone tell me what this sort of growth would be called?)

(After looking for variations of quartz growths, the closest I could find was called "cactus", but those seemed to grow outwards from the main original crystal, not paralell like in this specimen.
Also, after reading another topic here on the forum, where photos of epitaxy were posted.... would this be an auto-epitaxy ?
(according to Pete Richards definition, if I understood correctly... but not according to John S. White (a discussion I enjoyed))) :-)

[vic rzonca]

This is from the book by Harold L. Dibble, Quartz." Cathedral Quartz. One of the most common of these types is known as Cathedral quartz. These are crystals with the axes of the secondary crystals parallel to those of the main crystal. These clusters vaguely resemble smaller spires or buttresses around the main spire of a cathedral." More of a descriptive term than a scientific one. I guess everything has to be called something.

[Tobi]

Definitely two of my favourites:

[Heimo Hellwig]

Quartz from Goboboseb. Saw this specimen when visiting an elderly gentleman in the retirement village. He allowed me to photograph and post it on the Forum. Nicest local Quartz I have come across.

[Bob Harman]

Groups of tiny water clear quartz crystals showing free form growths adjacent to a calcite crystal. Self collected about 10 years ago.

[Tobi]

[James Catmur]

This seems to be an open Gwindel from Spain. We found this single specimen in 2007 in a small outcrop next to a vein of quartz. There were other quartz crystals but none like this. The crystal faces are parallel but there is a slight twist between the two crystals, which I only noticed today.

See what you think? Is it a Gwindel or just two almost totally parallel crystals

The locality where it was found is mentioned in Volumen VIII, Cuarzo y otros minerales de silice, Miguel Calvo Rebollar, p 243, top of the page where it says "La Presa".

[Bob Morgan]

Does this specimen have several Japan Law twins?
https://www.mineral-forum.com/message-board/download.php?id=72376

It resembles one that Jaroslav Hyrsl found with many twins.

[Bob Morgan]

The above post was in reference to Enrique LLorenz's Peruvian Specimen at the first of this thread.
https://www.mineral-forum.com/message-board/download.php?id=72376

As to the question about whether the double crystal immediately above is a Gwindel, I don't think so. The attachment would be on a prism face.

[James Catmur]

Bob

The attachment is a prism face - the two are attached to each other by their prism faces. That is why it had me confused - every face in each crystal has a parallel face in the other one, but there is about a 4 degree twist between them. So it looks like two totally parallel crystsls with a twist (clockwise) between them.

[Bob Morgan]

I can see your point and agree the divergence is reasonable as a gwindel. I was referring to the attachment to the matrix, which is usually along a prism face of one crystal. Still...?

[Josele]

[Bob Morgan]

I agree it's not a gwindel, even though it looks like there might be an a axis alignment at some spot. Very open gwindels can have some notched separation, but this would be too extreme.
There does appear to be a point of attachment on one crysrtal's pyramid, but gwindels grow out of the matrix along the a axis.

As to the Peruvian quartz, the possible twinning would be small deposition crystals on larger ones. That is very common from that locality, but can't be discerned from the photo.

[Josele]

Bob, you are right, many characteristics are not clearly visible in a photo, that's why I like to say "I think that ..."

Is true that high end and fine gwindel specimens usually show both terminations free of contact, with "c" axis more or less parallel to matrix surface, but there are also many samples that seem to be attached to matrix at terminations, with "c" axis penetrating into matrix, as can be seen in Gwindel Mindat Gallery

[Amir Akhavan]

Sorry to interrupt ;-) but I'd like to point out that a gwindel is not a composite or aggregate.
It's not made of stacked crystals and it has nothing to do with parallel growth.
Each gwindel started as a s i n g l e c r y s t a l that is elongated along and twisted around an a-axis.
That many gwindels and in particular open gwindels show sutures and that their tips fan out is a secondary effect of being overgrown by a layer of macromosaic quartz.
Amir

[Tobi]

A few more of my personal favourites from my collection that I want to add: