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This is a marcasite nodule. Straight from wiki: The mineral marcasite, sometimes called white iron pyrite, is iron sulfide (FeS2) with orthorhombic crystal structure. It is physically and crystallographically distinct from pyrite, which is iron sulfide with cubic crystal structure. Marcasite is lighter and more brittle than pyrite. Specimens of marcasite ...


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This looks to me to be graphite crystals in marble or quartzite. Based on your comment about the hardness I would probably go with quartzite. Highly metamophosed graphite can look metallic. Both the graphite and the calcium carbonate/quartz crystals are quite large indicating a long time spent at depth. Try to scratch the "metal" with a needle. If it is ...


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It looks to me like a breccia, where crystals of some mineral, perhaps tourmaline or olivine, have been scattered in a thin layer on the sea bed or the bed of a lake, and become welded together by minerals precipitated from the water. That would explain the thinness of the specimen and its straight,linear shape. Maybe a volcanic eruption in ancient times ...


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Stromatolite structure. The graininess a beat up or weathered limestone of some sort. But if it scratches glass it may be dolomatized limestone with some silica grains, enough to scratch glass. Stromatolite is often of chert but I haven't seen chert weathered like this. The layering looks like chert too. It's a puzzle.


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Stromatolite structure. The graininess a beat up or weathered limestone of some sort.


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The one on the left looks like sandstone or gritstone (gritstone is a coarse variety of sandstone), The rock on the right looks as though it might be slate, but more photos would be helpful. There is nothing dangerous in either type, but I wouldn't have thought they'd be much use for pigments. A much more promising material for pigment is mineral iron ochre,...


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Water is removed from gypsum hydrate about 300 F+ making it dry powder gypsum. Water is added to gypsum to make "plaster of Paris" , no particular temperature is involved. Not sure it answers the question , but gypsum commonly deposits in oil production tubing. The produced oil/water/gas mix cools as it comes up the well tubing and deposits in the tubing,; ...


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Granite is a light-colored igneous rock with grains large enough to be visible with the unaided eye. It forms from the slow crystallization of magma below Earth's surface. Granite is composed mainly of quartzand feldspar with minor amounts of mica, amphiboles, and other minerals. This mineral composition usually gives granite a red, pink, gray, or white ...


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Of the three categories of rocks, sedimentary, igneous and metamorphic, sedimentary is the closest type that coal could fit into. Coal was not derived from molten material, so is not igneous by definition. It was not transformed under temperature and pressure from a pre-existing rock into a metamorphic rock. Coal was lithified by compressive forces from ...


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The oldest geologic units in the study area are the Precambrian crystalline (metamorphic and igneous) rocks, which form a basement under the Paleozoic, Mesozoic, and Cenozoic rocks and sediments. The Precambrian rocks range in age from 1.7 to about 2.5 billion years, and were eroded to a gentle undulating plain at the beginning of the Paleozoic era (...


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I own this stone which was given to me as dinosaur egg (I'm vertebrate paleontologist). It weighs 2.9 kilograms and shows something shell-like. It's no dinosaur egg or something like this, it's a simple iron rich concretion which shows some shell-like erosion structures.


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I had a good geomorphology teacher. He was so good that I bought his book, published on Prentince Hall at 2008. He is an aged an experimented geomorphologist, so I totaly trust there is not an agreement about the physical origin of tafonies (or at least there wasn't an agreement at 2008 when his book was published). "Its origin [tafonis] is controversial (...


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This one is a simple concretion. The interior is mudstone, it is rich in iron, lending to it's orange-brown color. They are dense, very common and often made from a small organic material (a piece of a plant, shell or animal) rolling around in sediment and accreting material in a concentric pattern. Hence, when it hardens into rock and thus breaks, it breaks ...


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That is 100% a spark plug that has been melted. Without a doubt.


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It is called preferential weathering, but there is another element at play. Before the rock eroded into circular features, there were softer materials present. Those softer materials weathered away first leaving the more resistant host rock (or matrix) behind. The matrix is harder than the softer "clastic" material. When pebbles get washed into the cliff ...


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If the rock did not have the vesicles, I would say it is a komatiite as was suggested above. Because the vesicles are present, I agree with slag. The texture observed in the rock is called "spinifex" texture which is an irregular arrangement of tabular and acicular crystals, common in slag. https://www.researchgate.net/publication/...


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This is not a meteorite Meteorites will have a strong magnetic attraction, regmaglypts, fusion crust, flow lines and possible roll-over lips. This is a terrestrial rock. This was also not used as a primitive tool. There are no features that would indicate that. The flat surface is a natural break along the rocks natural plane of weakness. Meteorites will ...


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This is a quartz vein that has strong microfracturing and moderate hematite alteration. The fractures are filled in with hematite-rich fluids, which accounts for the red color. This is a good example of fluids filling in microfractures, which is a very common process in rock mechanics. The fracture-filling process occurs at depth within the earth's crust ...


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This is a quartz vein that has moderate hematite alteration. There is no feldspar in this sample.


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This looks man-made to me as well. The color is much too uniform across the entire surface and interior, which is typical of man-made material. Natural material would show gradation of some kind in a mass of this size.


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Agree with the first reply. It is flint. Also known as chert. The composition is Silica Dioxide (SiO2) which is the same composition as quartz. You'll get all different kinds of SiO2 out there with varying names based on the structures in the rock. Agate, chert, calcedony for example.


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It looks to me like a type of flint. Flint nodules are found in chalk and some types of limestone. By banging them with a hammer, you should be able to strike off curved chips with sharp edges. Fractures of flint typically show a conchoid (shell-like) curve. The interior of a flint nodule is brownish, with a glassy texture, but the exterior is often white ...


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Your rock is either a granite, a granodiorite, or a tonalite. If you look carefully, the grey bits are a bit translucent and look waxy. This is quartz. The white stuff sparkles slightly when you look at it in strong light from different angles. This is feldspar. The black stuff is either biotite mica or hornblende amphibole, but it's impossible to tell from ...


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Looks like deorite. It’s used around railroad tracks in my area. https://flexiblelearning.auckland.ac.nz/rocks_minerals/rocks/diorite.html


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