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Gerhard Niklasch
Joined: 27 Mar 2009
Posts: 134
Location: Munich
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Posted: Apr 21, 2009 15:23 Post subject: GN's selected items |
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Or, Some of the things that have caught my interest.
`Taking three as the subject to reason about...' let's have some sliced Tourmaline for starters! This is among the smallest pieces I have, and I do not know where it's from, though considering which stall I bought it from at the Mineralientage, it may perhaps be from the Transbaikal region of Russia.
We can see that it started out as a translucent, more or less triangular Rubellite, and later acquired a more or less hexagonal dark opaque overcoat. Also, it must have had a little triangular pedion face at one point, surrounded by three pyramid faces whose edges have left thin traces.
The second shot is a stereo pair. If you're new to these: hold a fingertip half way between your eyes and the monitor and look at it. Notice how your left eye now sees the image on the right behind your finger, and the right eye sees the image on the left; allow both images to blend into one. Gently remove your finger and without changing your crossed gaze, allow your eyes to re-focus onto the screen. With a little practice this will come naturally and succeed quickly...
Can you see that the various inclusions aren't all in one plane, and that the thin line from the triangle to the bottom right corner starts in the foreground and descends into the rearground? Also, notice the reflections on internal fracture or defect surfaces on the right, which are inclined in the opposite direction. If you look very closely, you'll see that the triangle in the middle is at the rear, with a smaller darker region in front of it.
This stereo pair was taken through my stereo microscope, using eyepiece projection, with both front and back lighting (halogen bulbs) if memory serves.
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Tourmaline slice, diam.23mm by 3mm thick, collection id 08xxT-001. |
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Tourmaline slice, diam.23mm by 3mm thick, collection id 08xxT-001. Stereo pair, field of view about 18mm wide. |
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Gerhard Niklasch
Joined: 27 Mar 2009
Posts: 134
Location: Munich
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Posted: Apr 21, 2009 16:07 Post subject: Re: GN's selected items |
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Few things are harder to photograph than a lustrous black tourmaline. A black tourmaline sees everything: the wooden furniture, the red curtains, the green plants, the yellow shirt and the blue jeans, and you can bet that at least one of its faces will reflect part of that rainbow into the camera lens...
Here's one of these black guys - indeed one of my first tourmalines. It's from Erongo Mountain in Namibia. This one has started growing a three-ray star of a different kind: still solid where the main pyramid faces meet each other, most of the volume between the edges is beginning to separate into a myriad of baby tourmalines.
All the babies still end almost in the same planes, so at first glance, it looks like a trigonal pyramid with pits. (In later growth stages, each baby would terminate at its own height.)
The bright reflections show that many of the babies on the two shadowed sides of the pyramid already have little faces parallel to the large brightly lit face at the top.
For more views (including details and stereo pairs), please see https://www.mindat.org/photo-225604.html .
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Tourmaline, Erongo Mt., Namibia. Diam. 53mm, height 28mm. GN's collection id 08NAT-001. |
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Carles Millan
Site Admin
Joined: 05 May 2007
Posts: 1471
Location: Catalonia
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Posted: Apr 21, 2009 16:23 Post subject: Re: GN's selected items |
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Hi Gerhard!
>Few things are harder to photograph than a lustrous black tourmaline.
Right! Shooting schorls is a real pain.
Be welcome to this forum section. I hope to see much more pieces of yours.
_________________ Al carrer Duran i Bas, si no hi vas no t'hi duran |
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Gerhard Niklasch
Joined: 27 Mar 2009
Posts: 134
Location: Munich
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Posted: Apr 24, 2009 11:47 Post subject: Re: GN's selected items |
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Many thanks for your kind words, Carles. Well my collection is still small, and I take images and process them from time to time as I get round to it. Your collection is, of course, a steady source of inspiration (and a constant target of admiration!).
It's been sunny today with a fine web of thin wispy clouds gracing the blue sky... an ideal occasion for taking a break from Tourmaline, and showing some Celestine. At 900g to the gram, this is one of the largest and heaviest pieces I have (so far). The vendor's label merely said `Madagascar'. Similar material is known, specifically, from the Sakoany mine in Mahajanga province; this specimen may also have come from there.
Most of the crystals are milky-blueish translucent, but a fingernail-sized part at the tip of one, conveniently sticking out at the corner, turns clear and transparent at a sharp boundary, and sparkles madly in the sun.
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Celestine, Madagascar. 110x90x75mm, xx to >40mm. GN's collection id 09MGC-001. |
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Celestine, Madagascar, detail. GN's collection id 09MGC-001. |
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Tobi
Site Admin
Joined: 07 Apr 2009
Posts: 4108
Location: Germany
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Posted: Apr 24, 2009 12:16 Post subject: Re: GN's selected items |
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Hallo Gerhard,
you wrote that the label says Madagascar and that the specimen may come from the Sakoany Mine. You can be sure: This Celestine is definitely from this mine. I've never heard of any similar Celestines from Madagascar, so you can be assured that it is from the mine near Sakoany in the Majunga province.
Liebe Grüße
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Gerhard Niklasch
Joined: 27 Mar 2009
Posts: 134
Location: Munich
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Posted: Apr 24, 2009 12:21 Post subject: Re: GN's selected items |
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But somehow I'm always drawn to three-fold symmetries...
I have no idea where my second Tourmaline slice hails from. Maybe I'll find out at the next Mineralientage (if the vendor still has another from this series). Madagascar might be a possibility - one among many.
In the first pair of images, notice how the wide green bands to the left of the central dark triangle become very narrow when viewed from a different angle: They are traces of former pyramid surfaces, and evidently we're looking from that side where the tip of this pyramid had once been.
A stereo pair is next, taken from the same side, but with the slice repositioned to have these bands at the bottom.
Third and fourth, under the microscope with both front and back lighting, some interior detail. We're now looking at the other side of the slice, straight up into the former terminating pyramid. The brown inclusions remind me of sea weed...
All of the lighter greenish-white area between the bands is really a stack of ultra thin green pyramid layers alternating with clear layers, like the growth rings of a tree - while the bands that were so obvious to the unaided eye came from much thicker layers. This can be seen in the final stereo micro pair: each growth layer has left a thin green line along the yellow fracture surface running left-right through the centre. (The three white patches on the upper surface, two at the top and one below said fracture, aren't inclusions as far as I can tell, but pits filled with residue of the polishing agent.)
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Tourmaline slice, loc. unknown, diam. 37 to 38.5mm by 2.9mm thick, GN's collection id 08xxT-002. Two views. |
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Tourmaline slice, loc. unknown, diam. 37 to 38.5mm by 2.9mm thick, GN's collection id 08xxT-002. Stereo pair. |
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Tourmaline slice, loc. unknown, detail. GN's collection id 08xxT-002. Field of view about 22mm wide. |
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Tourmaline slice, loc. unknown, detail. GN's collection id 08xxT-002. Stereo pair, field of view about 13mm wide. |
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Tourmaline slice, loc. unknown, detail. GN's collection id 08xxT-002. Stereo pair, field of view about 4mm wide. |
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Gerhard Niklasch
Joined: 27 Mar 2009
Posts: 134
Location: Munich
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Posted: Apr 24, 2009 12:27 Post subject: Re: GN's selected items |
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Thanks Tobias - that was also my impression after rummaging among the possibilities on mindat. Plus, an imprecise location on a label makes it likely that the specimen came from a prolific source, not from somewhere unusual that would have been worth mentioning.
Still, we just had a lively discussion on the mindat forum about the pitfalls of spurious specificity and the value of being very clear what's known and what's guesswork! :)
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Tobi
Site Admin
Joined: 07 Apr 2009
Posts: 4108
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Posted: Apr 24, 2009 13:59 Post subject: Re: GN's selected items |
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Oh yes, i know about this problem :-/ A lot of specimens came to me during the years, and many of them had just a vague information about the locality. When i buy minerals, of course i always look after complete and correct localities. But often you inherit a collection (or you just get some specimens as a gift) from another collector who didn't care as well about the correct localities. That's especially annoying when the mineral is something very beautiful (and potentially precious) like a large Fluorite or Calcite specimen. I often had to sort specimens out just because the correct locality was missing. That hurts when the mineral had the quality to become a really nice display specimen :-/
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Gerhard Niklasch
Joined: 27 Mar 2009
Posts: 134
Location: Munich
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Posted: Apr 24, 2009 14:38 Post subject: Re: GN's selected items |
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I'm not being religious about it - I sometimes buy things I like even if they come with incomplete information; and trying to find out more about their possible origins is often quite instructive...
Like this piece of Fluorite from a locality called `Mexico' which I picked up for 3 EUR some weeks ago. (I then went through all 31 Mexican states on mindat looking for Fluorite occurrences, and decided that the Tule mine was a probable candidate.)
Cubes, by the way, also have three-fold axes of symmetry :) as the truncated corner on the right illustrates. (The red-brown stuff above/behind it is an inclusion.)
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Fluorite, Mexico, 26x26x20mm, xx to 17mm edge, detail. Stereo pair, front and back lighting, field of view about 15mm wide. |
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Ed Huskinson
Joined: 15 Apr 2009
Posts: 318
Location: Kingman, Arizona
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Posted: Apr 24, 2009 15:11 Post subject: Re: GN's selected items |
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OK we can see the close-up of the nice purple fluorite. A view of the entire specimen, and another of the back-side to show the matrix, would help us with the locality determination.
Thanks GN.
Ed
_________________ La respuesta está en las rocas!! Estudiadlas!!
Ed |
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Gerhard Niklasch
Joined: 27 Mar 2009
Posts: 134
Location: Munich
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Posted: Apr 25, 2009 17:48 Post subject: Re: GN's selected items |
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Sure Ed! ...but I had to take these pictures first. (The specimen just happened to have wandered into a late-night microscope session before it met a convenient sunny morning...)
Here's a composite of views from four sides, with the above stereo micrograph taken from a fifth (the top). There is no matrix. The bottom is just a fracture / former contact surface.
The zoning (violet in several layers along the outside, mostly clear interior) is more pronounced in person than the pictures have captured, since I used no back lighting here.
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Fluorite, Mexico, 26x26x20mm, xx to 17mm edge, composite of four views. Diffuse daylight, plus fill-in flash in some of the shots. |
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Gerhard Niklasch
Joined: 27 Mar 2009
Posts: 134
Location: Munich
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Posted: May 10, 2009 13:09 Post subject: Re: GN's selected items |
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Calcium carbonate is the prototypical material of biogenic sedimentary rocks.
Olivine, red-hot and molten, is believed to make up the bulk of our planet's mantle.
So... what is it that brings both together in one and the same specimen?
...Metamorphism!
In particular, high-temperature metamorphism of impure dolomitic limestones. (Many limestones contain significant amounts of quartz or silicate impurities -- anyone who, like me in younger years, has been exploring the deep cave systems of the Picos de Europa can attest to their extreme abrasiveness. But I digress...)
So here we have, from a classic locality, a group of Peridot crystals of fine colour and frosted faces, with a backpack of translucent Calcite rhombs. (Magnetite is also present in dark, less than mm-sized, vaguely octahedral xx.)
I'm not sure how the belt running from top left to bottom right across the show side (and top right to bottom left past the Calcite on the back) has come about. It might reflect some tabular feature in the former matrix neighbourhood, or, perhaps more likely, it might be the result of the group having grown in a widening vein, torn apart and rehealing in the middle.
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Olivine series, Forsterite var.Peridot with Calcite; Sapat Gali (Soppat), Kohistan, Pakistan. 50x35x33mm, 56g. GN's collection id 09PKOcm01. Taken in direct sunlight. |
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Olivine series, Forsterite var.Peridot with Calcite; Sapat Gali (Soppat), Kohistan, Pakistan. 50x35x33mm, 56g. GN's collection id 09PKOcm01. Taken in direct sunlight. |
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Olivine series, Forsterite var.Peridot with Calcite; Sapat Gali (Soppat), Kohistan, Pakistan. 50x35x33mm, 56g. GN's collection id 09PKOcm01. Taken in direct sunlight. Stereo pair. |
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Olivine series, Forsterite var.Peridot with Calcite; Sapat Gali (Soppat), Kohistan, Pakistan. 50x35x33mm, 56g. GN's collection id 09PKOcm01. Taken in direct sunlight. Stereo pair. |
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Gerhard Niklasch
Joined: 27 Mar 2009
Posts: 134
Location: Munich
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Posted: May 10, 2009 13:53 Post subject: Re: GN's selected items |
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And a green apple from the southwestern corner of Mali... The Prehnite ball, with a ligher and a darker half separated by a sharp boundary, has grown around some kind of axial matrix support; a little crisscross group of Epidotes is attached to one side. (This association is common for the locality.)
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Prehnite and Epidote; Kayes region, Mali. Diameter 18-20mm, 14g. GN's collection id 09MLPE001. Taken in direct sunlight. |
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Prehnite and Epidote; Kayes region, Mali. Diameter 18-20mm, 14g. GN's collection id 09MLPE001. Taken in direct sunlight. |
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Prehnite and Epidote; Kayes region, Mali. Diameter 18-20mm, 14g. GN's collection id 09MLPE001. Taken in direct sunlight. Stereo pair. |
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Gerhard Niklasch
Joined: 27 Mar 2009
Posts: 134
Location: Munich
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Posted: May 10, 2009 15:09 Post subject: Re: GN's selected items |
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And while we're on the topic of green things...
This specimen unfortunately suffered some harsh treatment in transport, so much so that another plastic box in the same parcel was cracked. Astonishingly, the `grass' of tiny Malachite needles held up rather better than the naturally crumbly dolomitic matrix.
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Malachite needles on matrix; Tsumeb Mine, Otawi highlands, Namibia. 65x52x40mm, 184g. GN's collection id 09NAMm001. Taken in direct sunlight. |
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Malachite needles on matrix; Tsumeb Mine, Otawi highlands, Namibia. 65x52x40mm, 184g. GN's collection id 09NAMm001. Taken in direct sunlight. Stereo pair. |
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Malachite needles on matrix; Tsumeb Mine, Otawi highlands, Namibia. 65x52x40mm, 184g. GN's collection id 09NAMm001. Taken in direct sunlight. Close-up stereo pair. |
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Jordi Fabre
Overall coordinator of the Forum
Joined: 07 Aug 2006
Posts: 4899
Location: Barcelona
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Posted: May 10, 2009 15:12 Post subject: Re: GN's selected items |
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Gerhard,
I'm not sure about the right locality of your Fluorite: https://www.mineral-forum.com/message-board/viewtopic.php?p=4803#4803 but I would like to suggest Mina San Martín, Sombrerete, Zatatecas Mexico. Again, I'm not really sure about it.
Hopefully Peter can help.
Jordi
_________________ Audaces fortuna iuvat |
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Gerhard Niklasch
Joined: 27 Mar 2009
Posts: 134
Location: Munich
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Posted: May 15, 2009 13:56 Post subject: Re: GN's selected items |
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Thanks Jordi - yes, that was also one of the possibilities I'd come upon during my mindat trawl. Without any matrix it's hard to draw conclusions!
For today, something else entirely... a nice Quartz with a touch of Amethyst phantoms and a HUGE (relatively!) liquid inclusion and bubble, from the Brandberg district, Erongo region, Namibia (presumably from the Goboboseb mountains and specifically Tafelkop). I keep imagining that I can almost hear the bubble moving when I tilt the specimen this way and that...
In the close-up (second picture), it appears twice: once (its lower half only) seen straight through the front prism face, and again, raised and distorted to an ellipsoid by refraction, through the inclined prism face above it.
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Quartz (var. phantom Amethyst Enhydro); Brandberg district, Namibia. 72x43x~50mm, main quartz to 42mm, 94g. GN's collection id 09NAQm001. Taken in direct sunlight. |
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Quartz (var. phantom Amethyst Enhydro); Brandberg district, Namibia. 72x43x~50mm, main quartz to 42mm, 94g. GN's collection id 09NAQm001. Taken in direct sunlight. |
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Quartz (var. phantom Amethyst Enhydro); Brandberg district, Namibia. 72x43x~50mm, main quartz to 42mm, 94g. GN's collection id 09NAQm001. Taken in direct sunlight. Stereo pair. |
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Gerhard Niklasch
Joined: 27 Mar 2009
Posts: 134
Location: Munich
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Posted: Jun 14, 2009 17:18 Post subject: Re: GN's selected items |
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Among my lucky discoveries at the Munich spring fair in April, there were two tiny Aquamarines from somewhere in northern Pakistan (the Shigar valley would be as good a guess as any) which I picked out of a tray and got, by weight, for 2 euros (together). Admittedly I hadn't picked them quite at random - I had my 6x hand lens with me...
The first of these is neatly terminated at one end and has a number of growth channels extending from the interior to this end. A couple of them are open along a prism face, and partially filled with some white material.
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Beryl var.Aquamarine with growth channels; northern Pakistan. Diam. 9mm x 13mm. GN's collection id 09PKB-001. Taken in direct sunlight. |
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Beryl var.Aquamarine with growth channels; northern Pakistan. Diam. 9mm x 13mm. GN's collection id 09PKB-001. Stereo pair, taken in direct sunlight. |
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Beryl var.Aquamarine with growth channels; northern Pakistan. Diam. 9mm x 13mm. GN's collection id 09PKB-001. Stereo pair. |
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Beryl var.Aquamarine with growth channels; northern Pakistan. Diam. 9mm x 13mm. GN's collection id 09PKB-001. Stereo pair. |
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Gerhard Niklasch
Joined: 27 Mar 2009
Posts: 134
Location: Munich
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Posted: Jun 14, 2009 17:46 Post subject: Re: GN's selected items |
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The second of these Aquamarines was poorly terminated but had a few slender black needles inside it. My hand lens assisted guess was Tourmalines, but the microscope view did not bear this out: they are flat rhombs in cross section, some ending in apparently orthorhombic pyramids in the middle of the aqua body (I managed one mediocre shot), and others showing reddish broken endings.
The real surprise came when I spotted a few additional closed cavities, not unlike the growth channels in the former specimen but capped off and completely surrounded by the aqua. I racked up the magnification to 40x, and then saw the tell-tale meniscus shapes of liquid-gas surfaces in most of them! These bubbles are too large (relative to the holes they occupy) to move - they could only move by liquid evaporating at one end and condensing on the opposite side, or possibly by capillary flow along the walls.
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Beryl var.Aquamarine with inclusions; northern Pakistan. Diam. 7mm x 13mm. GN's collection id 09PKB-002. Taken in direct sunlight. |
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Beryl var.Aquamarine with inclusions; northern Pakistan. Diam. 7mm x 13mm. GN's collection id 09PKB-002. Stereo pair, field of view about 3.5mm tall. |
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Beryl var.Aquamarine with inclusions; northern Pakistan. Diam. 7mm x 13mm. GN's collection id 09PKB-002. Stereo pair, field of view about 2.2x4.4mm. |
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Beryl var.Aquamarine with inclusions; northern Pakistan. Diam. 7mm x 13mm. GN's collection id 09PKB-002. Stereo pair, field of view about 2.6x3.8mm. Same region as previous shot, but seen through the next prism face. |
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Beryl var.Aquamarine with inclusions; northern Pakistan. Diam. 7mm x 13mm. GN's collection id 09PKB-002. Stereo pair, field of view about 1.2x2mm. |
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Gerhard Niklasch
Joined: 27 Mar 2009
Posts: 134
Location: Munich
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Posted: Jul 05, 2009 16:34 Post subject: GN's selected items |
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One of the first items I picked up at Ste Marie-aux-Mines 2009 was this splendid sample of iridescent Goethite from Andalusia. I don't think this particular piece has appeared on a web page before, although many of its siblings have.
Almost the entire rainbow is represented.
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Iridescent Goethite; Tharsis, Huelva, Andalucía, España. 37mm tall. GN's collection id 09ESG-001. Taken in direct sunlight. |
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Iridescent Goethite; Tharsis, Huelva, Andalucía, España. 37mm tall. GN's collection id 09ESG-001. Stereo pair, taken in direct sunlight. |
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Iridescent Goethite; Tharsis, Huelva, Andalucía, España. 37mm tall. GN's collection id 09ESG-001. Taken in direct sunlight. |
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Iridescent Goethite; Tharsis, Huelva, Andalucía, España. 37mm tall. GN's collection id 09ESG-001. Stereo pair, taken in direct sunlight. |
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Gerhard Niklasch
Joined: 27 Mar 2009
Posts: 134
Location: Munich
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Posted: Jul 05, 2009 17:15 Post subject: Re: GN's selected items |
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Whereas the Goethite pictures almost took themselves, I have yet to think of a good angle for an overall view of the following specimen, a ~53mm group of clear-to-grey Dolomites from Navarra. There are also some interesting echelon-stepped faces...
For now, here's just a simple demonstration that one of the crystals is transparent enough, and unobstructed enough, to exhibit birefringence, calcite-like.
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Birefringent Dolomite (detail); Cantera Azkárate, Eugi (Eugui), Esteribar, Navarre (Navarra), España. Field of view about 15mm square. GN's collection id 09ESDm001. Stereo microscope, eyepiece projection, halogen + white LED illumination. |
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