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Identity HelpWhat is this, the triangle pattern.

2nd Jun 2015 07:47 UTCray richard

What's the triangle pattern on the big R face?

According "The Quartz Page", sometimes the M faces of a quartz with brazil law will show certain triangle patterns.

But in this case, these patterns displayed on R faces, so I dont know what is it.

Maybe some other minerals left those pits and then dissolved?

2nd Jun 2015 08:59 UTCDavid Von Bargen Manager

They are growth hillocks. Irregularities formed when the crystal grew.

2nd Jun 2015 12:16 UTCOwen Melfyn Lewis

Yep, as David said, growth features and not etch. You can check this for yourself with extreme oblique lighting and some magnification by observing where the shadows fall related to the features and the light position.

A puzzling feature is that the 'triangles' are not Euclidian, I.e. The sum of the interior angles is > 180 degrees because one or more sides can have a pronounced convex curve to it. If anyone knows why such shapes should form in this way, I would be grateful to know. Sometimes found in other mineral species, such as spodumene (see below).

Rock crystal (Herkimer type):

Morion:

Spodumene:

2nd Jun 2015 20:01 UTCAbdulB Sh

nice photos Owen, i have this Quartz with hillocks, but one thing is amazing about hillocks, there precise direction which is unchanged,

3rd Jun 2015 08:36 UTCray richard

Wow! Great Educational post.

All of above replier have enriched my mind.

Thank you!

5th Jun 2015 17:09 UTCDoug Daniels

Obviously Mother Nature didn't take Euclidian geometry when she went to school....

5th Jun 2015 17:46 UTCOwen Melfyn Lewis

True. Of more immediate interest, perhaps, is why simple crystal forms should build using some simple curves rather than the usual all-straight lines. I'm still struggling for an explanation.

6th Jun 2015 17:21 UTCD. Peck

I don't really understand this, but I do know that quartz has as a symmetry element a screw-axis in the unit cell. The silicate tetrahedra link to form a spiral structure that rotates either to the right or to the left (thus enantiomorphism - right handed or left handed) with the repeat distance within the cell being either 1/2 or 1/4 of c. As I understand it, in the transformation from beta to alpha as the quartz cools, the orderly helical structure of the beta is slightly displaced and slightly disordered yielding the alpha form. Intermediate between the two, an ordered structure of Dauphine twins that have a triangular prismatic structure parallel to the c-axis develops. I don't know whether this structure is ephemeral, disappearing as the alpha form stabilizes.

Another bit, I have read that atoms (silica tetrahedra?) can locate on a growing crystal surface in helical patterns. This makes sense to me especially for an enantiomorphic mineral like quartz.

Is it possible that the triangular hillocks are an intermediate relic of the transformation from the alpha to beta form and that the curved side of the triangle is the result of helical deposition? Are the curved sides of the triangles on the quartz always the same side, spatially? Would it make any difference whether or not it is always the same side? Does this explain the development of the curved lines/surfaces?

Or am I in deep water (or something else) and all wet?

7th Jun 2015 13:39 UTCOwen Melfyn Lewis

Welcome to the 'Wondering' club Don. It always good to meet another member. And it always seems worthwhile to me to attempt to extrapolate from what one does know to what one does not know, After all, if no one had done this - and successfully - , science could not have progressed so far, could it?

As far as I have yet seen, this growth form occurs with the following variations, which might give some clues as to their cause.

1. The classic 'trigon'. In the two lateral dimensions forming perfect equilateral triangles. In the third dimension ('height'), sometimes evidence of stepped growth. To my knowledge, only found on some crystals of the cubic system (diamond, spinel, fluorite) and some trigonal corundum. Never found (by me) in garnet.

2. A form found only (by me at least) in quartz - trigonal system with, as you say. a structural twist occurring within the unit cell. Two dimensionally, the impression is of isoscelean triangles but with both the equal long sides curved outwards by equal amounts (lesser curvature in the third 'base' side also possible. In the third dimension, growth always appears curved and not stepped. Typically, this growth form is always shallow (see Ray's no.1 shot and my morion (no.2) shot). I think other trianguloid forms also occur in quartz - but let's keep it simple for the moment.

3. Another and distinctive trianguloid form can be seem in spodumene (monoclinic system). Two dimensionally, this tends to a right-angled triangle but with the 'right-angle' being always about 87 degrees (setting the convex curve for the 'hypotenuse'). In the third dimension, pronouncedly curved on the 'hypotenuse' edge but less so on the other two edges.

One day all of this is going to speak some truth to me, I'm sure - if I live long enough and someone else does not get the revelation first :-)

7th Jun 2015 16:50 UTCD. Peck

Owen, I enjoy this kind of speculation . . . with the hope that it becomes knowledge. I know a bit about crystallography, but have a loooooooooong way to go. It keeps my aging brain active. I have to go look at your examples from other minerals. The thing that got me about the quartz is the development of a "mosaic" of triangular prisms parallel to the c-axis during the transition from beta-quartz to alpha-quartz.

7th Jun 2015 19:34 UTCEd Clopton 🌟 Expert

Re: Doug Daniels's post

It's probably more accurate to say that Mother Nature doesn't confine herself to Euclidean geometry, since nature in general and crystals in particular comtain lots of straight lines, planes, right angles, circles, octahedrons, etc. In fact, the fact that these forms all seem so "natural" is probably what got Euclid started in the first place.

Strictly speaking, the figures (curved triangles) that we are calling "non-Euclidean" here wouldn't bother Euclid, since by having curved sides they don't qualify as triangles at all and so are free to add up to anything they want. We're getting way off the track here, but truly non-Euclidean geometries are systems in which the interior angles of straight-sided triangles don't add up to 180° and parallel lines eventually intersect, something that requires curved space and things like that.

7th Jun 2015 20:12 UTCOwen Melfyn Lewis

Ed Clopton Wrote:

-------------------------------------------------------

> Re: Doug Daniels's post

>

> It's probably more accurate to say that Mother

> Nature doesn't confine herself to Euclidean

> geometry, since nature in general and crystals in

> particular comtain lots of straight lines, planes,

> right angles, circles, octahedrons, etc. In fact,

> the fact that these forms all seem so "natural" is

> probably what got Euclid started in the first

> place.

Euclid's elements are (as I seem to remember from the age of 13) a series of postulates and logically perfect proofs that are entirely devoid of any need to relate to natural objects.

>

> Strictly speaking, the figures (curved triangles)

> that we are calling "non-Euclidean" here wouldn't

> bother Euclid, since by having curved sides they

> don't qualify as triangles at all and so are free

> to add up to anything they want.

Well, I'd say otherwise. Rather, the lines deliniating the growth are not straight and and this prevents the area they contain meeting the the essential requirement for Euclid's postulate. But triangular figures they certainly are (if considered only in a single plane) albeit of a non-Euclidean kind.

> We're getting

> way off the track here, but truly non-Euclidean

> geometries are systems in which the interior

> angles of straight-sided triangles don't add up to

> 180° and parallel lines eventually intersect,

> something that requires curved space and things

> like that.

Well, I note there has been a subtle change in the way that at least one Euclidian postulate is now presented. As I remember it from 60 years ago, the Euclidian postulate of parallel lines is that, lines of infinite length are parallel if they meet only at infinity.

7th Jun 2015 23:48 UTCDoug Daniels

Let's not delve into mathdat now..... as I recall there is a branch of geometry/trigonometry with curved lines (hyberbolic?). I forget the name, it's been a few years. But, as Einstein said, "it's all relative" (OK, maybe he didn't say it...).

8th Jun 2015 03:08 UTCNorman King 🌟 Expert

Quartz isn't the only mineral whose crystals may have curved edges and surfaces. Diamond does it a lot. No helical stuff there (or is there?). I think we could come up with a lot of crystals having curves, many being isometric (silver, copper, fluorite, and so on), but including other systems as well (e.g., pyromorphite, descloizite, corundum, gypsum, dolomite). I'd bet there are several mechanisms by which that may occur.

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