Hot answers tagged

7

These are most likely manganese dendrites. It is not a fossil, and not organic. These usually form in cracks in rocks, and most likely this slab was broken along an existing crack. You can read more about it now: https://www.mindat.org/min-26645.html One comment: this is not basalt. Basalt is black. Most likely some form of limestone.


5

Your rock is a classic example of chert, one of the most common rocks on the surface of our planet.


4

Limestones are usually categorized following the Dunham & Folk classification. Only very rare or special limestones were given a name and these are often named after the location where they can be found e.g. Travertine. The images you provided are not very explicit which makes it literally impossible to clearly identify the limestone. Please consider ...


4

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 ...


4

Chlorine is a very reactive element. Contrary to your statement, chlorine occurs in many rocks and minerals. The mineral apatite, with the composition: Ca5(PO4)3(F,Cl,OH), is a natural source of chlorine. Virtually all rocks contain chlorine. Chlorine even occurs occurs in alkaline magmas. One of the most common minerals containing chlorine is common ...


3

Your rock appears to be quartz var. chalcedony (jasper) with the interior being quartz pseudomorph after another mineral probably calcite or aragonite. I've seen a number of quartz pseudomorph after calcite from Indiana over the years but I do not have a good reference for Indiana pseudomorphs.


3

Your rock appears to quartz stalactite with druzy quartz crystals coating a banded chalcedony. A nice little find but is probably not really worth much. Label it and put in a perky box, the specimen might fetch $1-2 US dollars. Quartz stalactite images.


3

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 ...


2

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.


2

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 ...


2

Based just on the pictures, it is quartz. If that is the case, a knife won't scratch it. Please see our guide for asking “Identify this rock” questions.


2

Why don't pyroxenites and peridotites appear on this diagram? Because they do not have any quartz, feldspars, or felspathoids. The same Wikipedia page also says this: QAPF diagrams are also not used if mafic minerals make up more than 90% of the rock composition (for example: peridotites and pyroxenites). Instead, we use a different diagram, that has ...


1

They are quite pretty, but they are not fossils. They remind me of the patterns that frost sometimes makes on window panes. A similar process is at work here, though with mineral bearing water infiltration rather than frost being the cause. The water infiltration deposits crystals in the rock.


1

The rocks are undoubtedly of volcanic origin, and I would attribute the marks on their surfaces to shrinkage while their interiors were still in a semi-molten condition but rapidly cooling. The white crystals are probably quartz.


1

See page 2 here for example: https://pangea.stanford.edu/courses/gp262/Notes/8.SeismicVelocity.pdf . What you refer to as Cp (as far as I can gather from your linked paper), is in the geophysics world generally referred to as the P-wave velocity (P stands for the primary/pressure/compressional wave; separating it from the S-wave which is the slower ...


1

According to this site: Chloride comes from underwater fumaroles (such as black smokers), whose smoke is the exhalation of the vapors that escape from the magma as it rises next to subsurface. There is very little Chloride in magma, less than 1% (of the gaseous content, which is a small fraction of the magma as well), but the massive volume of magma that is ...


1

Your rock is mostly like chalcedony, a micro-crystalline form of quartz based on texture and with small voids and crystals in the white portion. Typical conditions that produce jade rarely allows for voids in rocks.


1

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


1

This is not a rock but a mineral. A rock is a conglomerate of several crystals, usually of different types of minerals. A crystal is one single systematic structure of atoms. It would help to see the crystal from more than one perspective, but judging from the pictures available I suggest that is is gypsum. Wikipedia: Gypsum is a soft sulfate mineral ...


1

This is a nice example of a volcanic rock, probably an andesite or something related. The white crystals are plagioclase. The darker spots could be pyroxene, but I'm not sure.


1

It has been burned. No acidity etc. needed. If you throw one fist sized granit into a normal campfire (usually around 700 C) and leave it there to burn for some hours, when it cools it will crumble in your hands. As mentioned before "granite is made of crystals of different minerals" in intensive heat/cooling each mineral expands at a different rate and ...


1

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


1

Perple_X (http://www.perplex.ethz.ch/) is software designed to do exactly that. It has thermodynamic and mineral property databases for phases in interest. This is pretty much automation of method 3 given by the other answer. In short, the way it works: you input your bulk composition, pressure, and temperature, and it spits out the phase relations. A bit ...


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