Matt_Zukowski
Site Admin
Joined: 10 Apr 2009
Posts: 717
Location: Alaska
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Posted: Jun 03, 2012 23:39 Post subject: Chalcopyrite epitaxic on Tetrahedrite |
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The attached pictures show Chalcopyrite epitaxic on Tetrahedrite that I obtained from our fearless leader last Tucson. I welcome any comments (esp from Pete Richards) describing how the various textures on different faces of the tetrahedrite form. What is it about the structure of these two minerals that causes a "basket weave" chalcopyrite pattern on {111} faces and smoothly deposited chalcopyrite on {221} faces of the tetrahedrite?
BTW - does anyone know yet where these specimens are coming from? Someone told me that Bert Ottens was going to look into it.
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Chalcopyrite ep Tetrahedrite unknown locality in China 6.5 x 5.3 x 3.3 cm Note the "basket weave" texture of the chalcopyrite on the (111) face of the tetrahedrite at the lower left. |
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7401 Time(s) |
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Chalcopyrite ep Tetrahedrite unknown locality in China 6.5 x 5.3 x 3.3 cm The {111} face at the center right shows what may be a poorly developed "basket weave" pattern or perhaps some other texture for the chalcopyrite. |
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7392 Time(s) |
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Chalcopyrite ep Tetrahedrite unknown locality in China 6.5 x 5.3 x 3.3 cm Chalcopyrite ep Tetrahedrite unknown locality in China 6.5 x 5.3 x 3.3 cm On the center left, just above the calcite, you can see chalcopyrite smoothly covering the edge {221} faces of the tetrahedrite. |
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7379 Time(s) |
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Chalcopyrite ep Tetrahedrite unknown locality in China 6.5 x 5.3 x 3.3 cm The "basket weave" face is perpendicular to the page, facing upwards and to the left. |
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7400 Time(s) |
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Chalcopyrite ep Tetrahedrite unknown locality in China 6.5 x 5.3 x 3.3 cm A reflection off a smooth {221} face. |
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7359 Time(s) |
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Pete Richards
Site Admin
Joined: 29 Dec 2008
Posts: 833
Location: Northeast Ohio
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Posted: Jun 05, 2012 08:03 Post subject: Re: Chalcopyrite epitaxic on Tetrahedrite |
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It's hard to determine why the patterns on the different faces have different textures without seeing the specimen first hand. But generally I would guess that this occurs because the chalcopyrite has a different habit than the tetrahedrite, in such a way that on one set of tetrahedrite faces ({221}) the chalcopyrite faces are parallel, whereas on the other set of tetrahedrite faces ({111}) the chalcopyrite faces are inclined, forming a regular but non-planar surface.
Imagine a cubeoctahedron overgrown epitactically by many tiny cubes. On the cube faces of the host, the overgrowing cubes will present a flat surface that may very well fuse into a continuous plate. But on the octahedral faces of the host, the cubes will all be represented as little "pyramids", creating a rough surface. A tremendous amount of growth would have to occur selectively in the middle of these faces in order for the overgrowing cubes to fill out and become the corner of one large cube. Unlikely to happen!
_________________ Collecting and studying crystals with interesting habits, twinning, and epitaxy |
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