FMF - Friends of Minerals Forum, discussion and message board

[Josele]

Some quartz specimens from Tormik (Pakistan) are quite weird, with troubled growth, multiple terminations and unusual habit. This one has two peculiarities that baffle me:

1 - A semiperimetral inclined plane (I dare not call it face) that can see at top right. Seems be parallel to an "a" axis and cuts "c" axis with an angle clearly more obtuse than a rhombohedral face.

2 - Two parallel grooves seen at low center crossing four of the six prism faces. Planes containing grooves forms an angle with "c" axis similar to plane mentioned in point 1. Those planes seems to be almost parallel to another "a" axis but they not exactly match striation of prism face for about 2-3º.

Thanks for lend a hand.

[Martin Rich]

May be marks of preexisting calcite crystals?

Martin

[Dale Hallmark]

Maybe someone used a lapidary saw on it for some reason.

Dale

[Jordi Fabre]

[Pete Richards]

In some hydrothermal vein environments, and at least some other environments with temperatures much warmer that current conditions, early-formed calcite has a very flat, paper-thin morphology, called Papierspat (paper spar) in German. Other minerals, including quartz and fluorite, then form and grow around the edges of the calcite crystals, which later dissolve, leaving randomly oriented grooves and dents in the later-formed crystals.

I was recently looking at some fluorite from pre-Cambrian lava flows in Minnesota. The fluorite consisted of sub-parallel laths in vugs. The only sensible way to understand them was as what could grow between these calcite plates, and was left behind by their solution.

Some strange irregularly-polyhedral geodes ("polyhedroids") of quartz are similarly interpreted as partial quartz infillings of voids formed between such calcite crystals spanning veins in igneous/metamorphic rocks.

Sorry, no pictures.

[silvio steinhaus]

I have some similar quartz purchased from a prospector in Brazil, from the border of Minas Gerais to Bahia, unknown city.
The cuts in one of the samples looked me possible altered epidotes inclusions, which when cleaned with acid turned out to be totally removed.

[Josele]

Thanks for your very enlightening comments. Myself I have a piece from Bor Pit with these growth interferences but haven't found a relation before you pointed it.
What strikes me now is the fact that these calcite interferences in this thread and many more from this location seem to be in a similar orientation with respect to "c" axis of quartz, forming an angle of about 60º (regardless Silvio's one, which is a epidote interference). I wonder if this is a coincidence or may exist some sort of epitaxial-like reason for this.

[marco campos-venuti]

This crystal is from China. Interferences can be from Calcite, or maybe from Hematite?
They are also parallel as in the sample of Josele. Maybe better from Calcite.

[Pierre Joubert]

Fascinating!

[Clifford Trebilcock]

Interesting discussion ! A few years ago I came across a small Quartz crystal seam in some metamorphosed schist not far from my home here in Phippsburg, Maine. The crystals look similar to some of the Dalnegorsk Quartz crystals, but on a smaller scale. Some look like stacked coins or caps on stems. Attaching a couple of photos of one specimen.

[John S. White]

I have long been fascinated by these quartzes which do indeed appear to owe their strange forms to having grown among and around calcite crystals, with the calcite subsequently etched away. However, I was fortunate in having acquired one specimen from the Bor mine in Russia which still contained much of the calcite, see photo. My favorite specimen from the Bor mine is the small one which appears to have grown through a hollow "tunnel" in calcite. At one time these were quite common but are now difficult to find. Finally I am including an example from China, similar to the one shown above, and in my opinion there can be little doubt that calcite influenced the development of these crystals. I do not believe that the angle of the "cuts" in the quartz is constant. I believe it is completely random.

I apologize for the very poor photos. They were taken in great haste.

[Pete Richards]

One thing that is interesting about Cliff's specimen and John's last specimen is that one can envisage a single calcite plate inflluencing several well-separated quartz crystals!

[Pete Richards]

Here's a specimen I just obtained - almost more groove than quartz!

One interesting thing about this specimen is that the planes preserve a texture of lines or striations that is consistent with the c-axis of calcite - three sets of lines forming equilateral triangles.

Another is that there are two additional sets of grooves oriented in different directions from the main one. Two sets are obvious in the last image. The third one is nearly in the plane of the image, and its location is indicated by the black line drawn just inside of the trace of the groove itself. None of these three directions is parallel to the faces of the quartz.

This crystal is so torn up by the grooves that I cannot figure out what its orientation is!

[Josele]

A pretty piece! For sure you will find the orientation of the quartz crystal if you spent some time mulling over it. Please, let us know when you find out.

[Jared3339]

Very pretty in my opinion.