# Tag Info

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The reason minerals like quarts and diamonds vary in color is generally caused by the chemical elements involved while the crystal is being formed. Chemicals Different colors can be created by different chemicals. Amethyst for example has traces of iron built into its crystalline structure giving it a purple hue. Iron can also give crystals a yellow hue. [...

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Yes, it is real. Whoever took the photo, congratulations on a very fine image. I have never seen this texture on such a scale, but something similar can be achieved in the laboratory by creating a bubble membrane of pure super-cooled water and blowing a few dust nuclei onto the surface. A comparable geometry appears very rapidly. The size of the ice crystals ...

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The premise of your question is entirely wrong. There are many examples of sharp corners in nature, the most obvious being well formed crystals. Pyrite is a classic example that was mentioned by @wienein in the comments. In a ideal situation it forms cubic crystals with sharp edges. A classic non-crystalline example would be volcanic glasses such as ...

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The hardness of minerals is diagnostic because the hardness is determined by the strength of bonds and the structure of the mineral lattice. Hardness is basically the stress required to create and grow extended lattice defects such as micro-fractures, stress twins, and dislocations. Diamond, quartz, and framework silicates, such as feldspar, are hard ...

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Double-terminated crystals can from by crystallizing from a melt. The crystallization nucleus has to float freely in the magma chamber. As long as no other crystals obstruct the growth the crystal will grow in its own characteristic form (euhedral). This happens for example with feldspar crystals. (Example: http://www.erdwissen.ch/wp-content/uploads/2010/12/...

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This picture was taken in what seem to be a small pond, of very calm water. It seem that in ideal conditions, implying but not limited to : absence of winds clean water eg: no nuclei to provide an anchor for crystal formation low temperature gradient between air and watrer (air almost near 0 °C and very slowly falling) ice grain can grow quite large. This ...

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I'd like to elaborate of the Chemicals issue of Azzie Rogers' answer. You can divide the chemical coloring into three main parts (there may be more, but these are the important ones): Inclusions A large, solid crystal can have tiny inclusions of other solid minerals. Commonly these inclusions are too small to individually observe by the naked eye. ...

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All unit cells are parallel-sided hexahedra. These are six sided shapes with parallel opposite sides. Their three principle angles may or may not be 90 degrees. And the three side lengths may or may not be equal. All of these unit cells can be uniformly stacked. Using these building blocks it is only possible to produce planes of reflection, diads (axis of ...

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This is not a four- digit number but four separare numbers called Bravais-Miller indices. Bravais-Miller indices descrive the orientation of a crystal plane relative to the symmetry axes of a crystal, as described in Wikipedia. Put very briefly, a zero index means the plane is parallel to that axis, while nonzero indices encode the relative values of the ...

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Not sure this is appropriate for Earth Science SE (Chemistry SE would be a better fit), but the answer is "maybe". quoting from the same Wikipedia article: Three oxides of xenon are known: xenon trioxide ($\small\mathsf{XeO_3)}$ and xenon tetroxide $\small\mathsf{(XeO_4)}$, both of which are dangerously explosive and powerful oxidizing agents, ...

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I'm pretty sure a more rigorous answer deserves to come along, but I can give a simple overview of some of the important factors. Cleavage planes have to do with bond strength and bond geometry. If there isn't a plane of bonds that can be cut through, then you won't get cleavage. When a mineral is fractured, the fracture "wants" to take the path where the ...

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There are some subtleties that I'd like to add, in addition to Mark's answer. When talking about the hardness of a mineral, the nature of the chemical bonds in the crystal structure (e.g. covalent vs ionic) are not the only important thing. Crystal morphology is also important. For example, Si-O-Si and Al-O-Al bonds usually cause minerals to be hard, such ...

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The color of a mineral can be caused by a variety of mechanisms. This is also true of amethyst, which is a variety of quartz ($\ce{SiO2}$), and can be found in many colors. The major factors responsible for the production of color in minerals fall into five categories: The presence of an element essential to the mineral composition The presence of a minor ...

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They are not synonymous. Cleavage means breaking along planes defined by crystallographic directions. For example, cubic crystals like halite, NaCl, often cleave along directions that follow the cubic form. However, with a different bond strength, like fluorite $\ce{CaF2}$, the crystals cleave most easily along octahedral directions, similar to two ...

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Should one assume that the mineral petitjeanite and the chemical discussed in the recent Chemical & Engineering News article Photocatalyst shreds drinking water contaminant PFOA are probably the same crystal configuration and unit cell, or can there be some variety? No you cannot assume the structure from the formula, many materials have polymorphs (...

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If "oblique square prism" is this, where the top and bottom planes are parallel, then yes, there are. Carbonates (members of the Calcite and Dolomite, but not Aragonite, groups) have perfect cleavages that leave them with such habit. But be warned that they do not crystallize with such habit, it is a product of an effort that forced it to break accordingly ...

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Your question is much more complicated from mathematical point of view than it seems to be. First, I'll start with a nice photo: (source: Wikipedia). What you see is really a photo and it is almost a mono-crystal. The only problem is that we all know that it cannot be a monocrystal since it cannot tile the space. So what is it? A quasicrystal -- matter with ...

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Q1: A volcano consists of many lava flows that occur over a long period of time. In general, only very few of these lava flows have the right composition and the right cooling history that are required to form obsidian. This is why only parts of a volcano consist of obsidian, and by volume it's a generally a very small amount. Q2: And yes there is ...

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In particular, in season 7 of Game of Thrones, the island of Dragonstone is revealed to contain a veritable mountain of obsidian - is such a thing possible in the real world? I would have thought that, above a certain volume, the center of the mass would be well-enough insulated so that crystallization could occur, spoiling the obsidian. Sure, an island of ...

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Silicon carbide is covalent and can be synthesized at atmospheric pressure by the Acheson process. Temperatures may actually be somewhat higher than your range but are easily achieved by the process. 1,4 dichlorobenzene (used in moth balls) is a compound that forms crystals at low temperatures. I think the molecules in the crystal are joined only by weak ...

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I think the commenters have identified the issue. Halite does not have perfect cleavage along the {110} plane. As recorded in Mindat, Halite has perfect cleavage alone {100}, {010}, and {001}. This makes sense, as Halite is a cubic mineral (fcc), these are the planes you would expect it to cleave on.

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Double terminated crystals normally form in free floating pockets of liquid that slowly evaporated, leaving perfectly formed crystals with terminations on both sides. Unlike usual quartz formations which grow in igneous rock, double terminated crystals are more than likely found in sedimentary rock laid down by subterranean marine deposits a long time ago. ...

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Yes, it has. Cody & Cody (1998), Journal of Sedimentary Research. http://archives.datapages.com/data/sepm/journals/v55-58/data/058/058002/0247.htm Abstract: Gypsum crystals were grown in experimental conditions analogous to saline terrestrial environments within bentonite clay gels by diffusion control at three different temperatures, four ...

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Yes, it is rose quartz. There are a number of mines in eastern New York near Vermont where rose quartz been found. Massive rose quartz can occur in granitic pegmatites. I could not google to find images of any massive rose quartz from the northeastern United States but it is very similar in appearance to the rose quartz from Black Hill of South Dakota. The ...

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Are your stones raw or are they cut & polished as they would appear if mounted in jewellery pieces? There are tests such as streak & hardness which can be done to raw stones but not to polished stones because these test would damage the polished surface. There are a number of websites that can be used, such as: Rock Identification Made Easy Rocks: ...

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Geodes form where there is a gas bubble or some other sort of cavity in volcanic or sedimentary rocks. I once found scores of them eroding out of a sea cliff in Oman, and they looked very similar to yours. I can tell that your geode was formed in sedimentary rock like mine were. What happens is that over millions of years, water seeps in, sometimes bringing ...

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Having the same formula does not mean that the crystal structure is the same. An example is calcium carbonate, which can form the minerals calcite or aragonite. So you have to read the publications to know if they have done X-ray diffraction to positively identify the crystals as petitjeanite. If that is the case, then the crystal structure is triclinic and ...

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