Questions tagged [rocks]

Questions about rock types, formation, chemistry, and physics. If you just want help identifying a rock please use the tag "identification-request".

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3
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1answer
97 views

What rock is this that I found on beach? [closed]

Found this on the beach in NY - it is a dark red colored rock with the green stones:
6
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2answers
2k views

Why are most minerals so rare?

There are 4,660 known minerals, so why are most of them so rare? Is it to do with the structure of minerals?
10
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1answer
484 views

Are “monoliths” giant, isolated rocks sitting in dirt, or are they continuous with bedrock

I am at a loss for the precise, correct terminology, but I have read in Wikipedia that Uluru is not a monolith, but Savandurga is, and that I probably shouldn't be using the word monolith to begin ...
5
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1answer
335 views

What are the circular features in this rock? [closed]

I found this rock by the shore of Lake Ontario. It's light weight and it was grouped with some other rocks with the same patterns.
2
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1answer
362 views

Please help me identify this very cool rock with a face [closed]

I found this rock where there was a lot of petrified wood but this does not resemble any of the many pieces of petrified wood that I have collected. It has the shape of a face, in my opinion. It has ...
5
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1answer
384 views

I'm trying to find the name of this rock [closed]

I found it upstate New York... Can someone please help me identify this rock. I added photos with different lighting. It's a very dark purple with a mix color showing more in the center. Its very soft ...
8
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1answer
940 views

Rock ID: brittle black/white w/ crystals & mica-like cleavage layers, Raleigh, NC, USA [closed]

Where it was Found: I found the rock laying on the sidewalk near some landscaping at my apartment complex in Raleigh, NC. Size: The largest intact portion of the rock is about 2.2 cm in diameter. ...
4
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1answer
430 views

What rock is this? [closed]

I've had this little guy for a while now and have been trying to identify it for some time with no luck. It looks like its oxidized with tiny little crystals, but it's hard to tell for sure. Any ...
10
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2answers
17k views

How long does it take for a stone to alter?

We see stones and they appear to be the same throughout our life time. Mountains also appear to not significantly change. So do mountains and stones decompose? What is the life span of a stone? After ...
1
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2answers
732 views

Does grade of metamorphism apply to igneous and sedimentary rocks?

Does grade of metamorphism apply to igneous and sedimentary rocks? I know that grade of metamorphism applies to the scale in which a rock becomes crystallized. Or is it? Please also define grade of ...
3
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4answers
3k views

When metamorphic rocks undergo pressure, how are they changed?

When metamorphic rocks undergo pressure they are changed, but how are they changed? Do they become fragments of rocks? Doesn't that mean that the difference between sedimentary rocks and metamorphic ...
4
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1answer
426 views

Any idea what are these circular rock marks?

During a family trip in the Israeli National Trail in the Pora Stream part (31.496871, 34.770928), I noticed these circular rock marks. Any idea what are they?
2
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2answers
440 views

Was there once a glacier over Starcke national park in Queensland Australia?

I was randomly exploring Google Earth when I came across some sort of rock formation in northern Australia. The location of the rock formation with respect to Australia is shown below. It is in or ...
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1answer
81 views

Color in Gems and Rocks [duplicate]

Why is it that gems/ rocks, such as Ruby, Sapphire, Topaz, etc... all have their own unique colors? Is this something that happens from chemical attraction with each stone upon formation?
4
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1answer
167 views

Is this a rock? [closed]

My son found this in our front yard. We live in Richardson, TX. It is brittle and little gold flecks fall from it when you handle it. The darker smooth parts are like a mirror. The clear part at the ...
4
votes
1answer
147 views

Can anyone identify this stone? [closed]

I found this rock at the weekend in the forest of Haigh Hall, Standish. It seems to be a solid mass of fibrous material. I have given it a scrub with warm water and a toothbrush just to get rid of ...
0
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1answer
588 views

The rock that gives birth to quartz sand

Thanks to one minute of the Earth we know that beach sand mother rock, besides the quartz itself, is (or was?) made of olivine, amphibole and orthoclase. I wonder, what is the name of that rock and ...
0
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1answer
161 views

Rock ID: Bone and potato-shaped, copper-colored [closed]

I found these two intriguing rocks on the UK's seaside. They have an unusual potato shape and copper/green color. Whrn knocked against each other, the sound is clear, metallic and the vibrations keep ...
7
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3answers
2k views

How was this egg shaped rock made and what is it? [closed]

The following small egg-like rock was found laying on the ground in Tampere, a city in southern Finland. It weights about 950 grams, has a volume of about 360 cm3 and thus a density of about 2600 kg/...
1
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0answers
132 views

Can you help me identify this rock? [closed]

We found this in our back yard (in Michigan) while digging one day. I'm curious about it, it seems different than others we've found. It's a pretty good size, about the size of a basketball.
3
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0answers
120 views

How Common is Volcanic Tuff?

Volcanic tuff was a key material in the Roman invention of concrete, something that modern concrete, or "Portland cement", lacked. With tuff, not only would Roman concrete be waterproof, it would ...
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0answers
46 views

Weathering of silicates

I am trying to find a relationship between the silicate-rich rocks weathering products. For example I've found information regarding gabbro weathering in which, according the consulted source, in 100 ...
2
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1answer
174 views

Ions & elements, which is the correct terminology to use when discussing chemical compounds in Earth Science?

Different textbooks use different terminologies when discussing the same chemical compounds, for example when discussing the minerals... Elements / Compounds Sulfide minerals consist of metallic ...
0
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1answer
2k views

How long will it take for the ocean to erode Rockall?

Loosely related to the question Will the ocean eventually erode all land?: How long will it take for the ocean to erode Rockall (an uninhabited granite islet within the exclusive economic zone of the ...
4
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2answers
893 views

How this sedimentary rock is made?

Apologies in advance for a beginners question. Different rock types make me curious and recently went to an area where interesting sedimentary rock is all over. As the area is on the coast, sea has ...
0
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1answer
50 views

Is there any covalent crystals that can be easily synthesized?

I am looking for a kind of crystal that can be artificially made at relatively low temperatures (below 1500 degree Celsius) and relatively quickly (not geological time). The product is ideally ...
1
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1answer
249 views

Why do manganese nodules have different constitution than sea water?

Analysing the constituents of manganese nodules, we find that the relative proportion of minerals differs from that of the surrounding sea water. Can someone explain to me why the proportion of the ...
6
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0answers
165 views

Basalt vs. columnar basalt

I recently visited a cliff on the south coast of Ulva in the Inner Hebrides where there are ~10m thick flows of columnar basalt. The columnar basalt forming most of the cliff is sandwiched between ...
3
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0answers
49 views

Link between different ways of modeling permeability

The most famous equation describing the permeability $k$ of a soil is the Kozeny-Carman equation: $$k = \frac{\phi}{8}r^2 \approx \frac{\phi}{c}\left(\frac{V}{S}\right)^2$$ $\phi$: porosity V: pore ...
2
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0answers
645 views

What type of rock is this powdery white rock with a fairly smooth dark shell and rusty patches I found while digging up pipe? [closed]

This rock is sort of a dark grey/black and kind of shiny but more matte I'd say. It does have some brown rust-like spots on it. And the inside has little dimples in a what seems to be more chalky ...
5
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1answer
127 views

Strange coating in old lime mine shaft

Near Prague,Czech Republic is old lime mine. Most of it is closed but one short transport tunnel under one hill is publicly accessible. Tunnel has profile around 2,5x2,5m and it's slightly bended and ...
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0answers
401 views

What does a negative value for the inclusive graphic standard deviation mean?

I'm calculating the inclusive graphic standard deviation for sediment from a cumulative frequency graph, with this formula: But when I plug in the numbers, I get a negative value, because my ranges ...
9
votes
3answers
653 views

What do you call boulders of non sedimentary rock that were lithified into sandstone?

I'm convinced there is a word for this. I was in the Hoodoos at Writing on Stone this weekend and kept noticing what looked like reddish quartzite boulders laying around in the sand, or sometimes ...
1
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1answer
71 views

What type of mineral is this? [closed]

My grandfather found this thing.
2
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1answer
80 views

Unknown semi-precious stone [closed]

On the handwork market I've found piece like this Merchant (who was reseller) didn't know its name. Have you any idea what is that? EDIT: I think it was about 5 on Moch's scale. It was black with ...
7
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2answers
2k views

Rock ID: Geode, soft, dull black exterior with crystal inside, from Snæfellsnes, Iceland [closed]

My fiancée found this on a recent trip to Iceland, on Snæfellsnes peninsula - she spotted the sparkle of the crystals among the abundant black, grey, and dark red rocks. There is a roadside vista spot ...
4
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0answers
572 views

Definitive values that classifies a rock as having “low”, “medium”, and “high” -strength, -hardness, -toughness, and -consolidation?

Question: Are there any widely accepted published values (or ranges) that classifies a rock as having “low” “medium” “high” -strength, -hardness, -toughness, and -consolidation (cementation or ...
4
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2answers
843 views

Can you confirm if this rock is sandstone - it is this from Cape Cod, MA, USA [closed]

A few years ago I found this unusual looking rock while walking around the beach of Cape Code, MA, USA. My guess is that it is sandstone, but I didn't see any others like it on my stay. It is has ...
3
votes
1answer
595 views

Does flow banding only occur in silicic rocks?

I made a video about what I learnt in my A Level Geology course so far, about igneous rocks. One thing I mentioned was that flow banding is mostly only found in silicic rocks (and so mostly rhyolite) ...
4
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1answer
180 views

Why pro-gradation occurs along coastal environments?

I am currently studying the deposition process in coastal environments and I came across a point which I do not understand concerning grading of grain size. According to "Petroleum Geology by North F....
8
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2answers
658 views

What kind of a rock is this (from Finland)? [closed]

I found this rock at my friend's summer cottage in Finland. I have never seen a rock like this in my life. It resembles a lava stone, but Finland isn't a volcanic country. I am no expert in geology ...
1
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2answers
525 views

How are natural specimens, such as ‘Moqui Marbles’, distinguished from man-made artifacts?

If a particular type of rock specimen is found throughout Earth and is made entirely of natural minerals, but the individual specimens differ minutely from another in size and shape and look to be ...
3
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2answers
388 views

Growth identification on obsidian needed [closed]

What are the small white growths on my obsidian? And does this specimen look odd or rare?
2
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2answers
107 views

Describing this rock [closed]

Is this rock granite? Can anyone help me identifying this rock and describing it?
6
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1answer
803 views

Rock identification: meteorite or lava? [closed]

I was told by a crystal quartz store owner it was a type of lava rock but I have high doubts. hardness: diamond size: 4'' $\times$ 4'' weight: 1.5 lb location: unknown smell: sulfur trait: ...
2
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3answers
221 views

A human foot impression on a rock

There is a rock that I have been climbing ever since I was a kid to get a magnificent view of an escarpment. One of the things that was part of our rock tour among other things was a perfect human ...
3
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2answers
660 views

Rock identification: opal or crystal? [closed]

I picked this up from a good friend, he didn't have any information but someone said it was an opal and not a crystal. It is see-through like foggy glass in some spots. hardness rated as quarts size ...
5
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4answers
6k views

Why is coal classified as a sedimentary rock?

Something just clicked in my head today. Rocks, by the definition I was taught, are composed of minerals which in turn are by definition not organic, so they are or were not alive. However. Coal, ...
6
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1answer
1k views

How to identify a predator's coprolite from an herbivore's?

I have a coprolite that is 8" by 5" and weighs 8 lbs. The shape is similar to a lumpy brain, the colors below outer crust are deep red and the crust is pastel green and grey. It has a strong density ...
6
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1answer
455 views

Is this iron ore? [closed]

Is this iron ore? I found it in the back yard in Western Australia few years back; it has a roughish surface. It was sticking out of my grass. It has sand grains stuck on it. It is reasonably hard, ...