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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129 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.
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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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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 ...
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1answer
163 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 ...
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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 ...
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2answers
750 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 ...
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1answer
42 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 ...
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1answer
240 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 ...
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0answers
161 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 ...
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1answer
457 views

What type of rock is this and how did it form?

I'm looking for some help identifying this rock. I'm also interested in finding out how it is likely to have formed. I found it on a black sand beach in Vik, southern Iceland, not far from the ...
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47 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 ...
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567 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 ...
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1answer
115 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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369 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 ...
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2answers
79 views

Question about Type of Rock

Could anyone tell me what kind of rock this is
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3answers
603 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 ...
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1answer
70 views

What type of mineral is this? [closed]

My grandfather found this thing.
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1answer
78 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 ...
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1answer
847 views

Rock ID: a black rock/lava? around another white rock, unknown location

I tried to look for any similar rocks on the Internet but couldn't find anything and I don't know much about geology. I've been given this rock when I was a child and now I'm just curious to know ...
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3answers
744 views

What kind of rock or mineral is this?

I found this rock or mineral in our backyard, and I'm having a hard time trying to figure it out. Does anyone know exactly what this thing is
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2answers
2k views

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

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 ...
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0answers
523 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 ...
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2answers
764 views

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

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 ...
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1answer
512 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) ...
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1answer
178 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....
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2answers
630 views

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

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 ...
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1answer
222 views

stalagmite Identification and formation process needed

I can not find a similar image or info on the net to identify my presumably Cave stalagmite. I would like to know where and how it formed. Now the black interfiling i'm assuming to be water that ...
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1answer
196 views

Unusual rock identification needed

This was found near a river on sand with the green side down. The first picture of the rock has a glossy finish. The second image has a high green color that resembles a crust layer involving heat of ...
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2answers
502 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 ...
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2answers
356 views

Growth identification on obsidian needed

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

Can anyone identify and describe this rock?

Can anyone help me identifying this rock and describing it? Saw this today while driving.
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2answers
102 views

Describing this rock

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

Rock identification: meteorite or lava?

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: ...
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3answers
215 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 ...
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2answers
598 views

Rock identification: opal or crystal?

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 ...
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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, ...
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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 ...
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2answers
668 views

Rock ID: Large, heterogeneous, magnetic rock in Cascade Range, Washington, USA

I found this rock in a glacial till in north central Washington State, on the east side of the Cascade Range. The dark round crystals are roughly 1 inch (2.54 cm) by 2 inch (5.08 cm) in size. The ...
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1answer
393 views

Is this iron ore?

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, ...
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4answers
2k views

What sort of rock is the large polished boulder?

This large polished boulder sits outside one entrance the University College Hospital in London: Here is a close up: What sort of rock is it and how would it have formed?
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2answers
667 views

What type of rock is this paving stone and what is the origin of the red colouration?

This paving slab is part of the floor of the new atrium in Kings Cross Station in London: The paving slabs are mostly grey but some contain areas of this reddish colouration. They are all fine ...
8
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1answer
616 views

We found this rock and we don't know what it is

I found these rocks at a road in Sweden. They are different from the other rocks used for the road. The hardness is higher than 5.5 as the rocks aren't affected by a knife. the size is 2.0-2.5cm ...
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2answers
850 views

How to learn the different types of rock

I would like to be able to point to a piece of rock and say that is rock type such and such. I have tried learning but it literally seems like an endless list of types and sub types and the pictures ...
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1answer
209 views

What could have formed the pattern inside this piece of siltstone?

I have what i think is a piece of siltstone with an interesting pattern on the face. It looks like a lichen or lightning bolt, as shown in the picture. The interior of the pattern is the same color as ...
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2answers
288 views

Can rocks have pressure signatures?

Since rocks can have magnetic signatures, as is the case with paleomagnetism, can they store past pressures also? For example, when researchers are trying to determine past ocean levels, they ...
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1answer
526 views

What kind of rock is this (from UK)?

What kind of rock is this? It was found in Threemilestone, near Truro in Cornwall, UK. The rock has a hardness of over 5.5, as a knife doesn't scratch most parts of it. It is 10cm across the top, ...
4
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1answer
669 views

How to find rocks worth tumbling?

My son recently got a rock tumbler and I was wondering if anybody knows of any resources that would show pictures of the different types of rocks as they would be found on the ground. I live in Chino ...
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2answers
2k views

What are the most common minerals at the Earth's surface?

I know how to find out the first few most common minerals, and I know how to find a list of 6800 minerals that one geologist found as a microscopic grain in this one meteorite. I can't seem to find a ...
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4answers
14k views

What was the first rock in the rock cycle?

I am an undergraduate student but I am a tutor at a High School, and one student asked me. Attempting to explain the rock cycle "if one rock turns into the other then which came first" my gut is ...
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1answer
108 views

The differences in gases produced by asteroids impacting crystalline and sedimentary rocks

A second question inspired from How Long Will Life Last On Earth, The Manicouagan crater in Canada is one of the largest impact crater on Earth. It was created 215 million years ago, but its ...