Questions tagged [rocks]

Questions about rock types, formation, chemistry, and physics.

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How do these holes form?

I was casually browsing the google earth street view map today. And I noticed strange cavities in a rock wall on Henderson Island, a coral island in the South Pacific. What could have caused this to ...
Thomas Peng's user avatar
2 votes
1 answer
69 views

Subantarctic islands: man-made rock cairn or natural formation?

When surveying penguin colonies on subantarctic Antipodes Island, we found a cave that features a strange rock formation: The formation does not appear to be particularly exposed to the elements so ...
Tomm's user avatar
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2 answers
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Are there enough rocks that are useful to burn that Paleolithic people would have experimented with them?

I'm not sure where to ask this question, but I thought there might be people on this list who are familiar with rocks and minerals. I've been thinking about the first smelting of ore (which seems to ...
David Gudeman's user avatar
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26 views

How to extend the Wyllie time average equation to multiple constituents

I understand the Wyllie time average equation How to extend it to multiple constituents ?
Sagar Rawal's user avatar
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60 views

Are These Leaf Fossils Found Near a Texas Lake Shore?

I recently came across some intriguing specimens near a lake shore in Texas and am seeking your expertise to help identify them. The objects have a few characteristics that lead me to believe they ...
user3424230's user avatar
13 votes
1 answer
2k views

Why is basalt denser than granite?

If lava is nothing but magma breaking through the earth's surface, then why is basalt more dense than granite? I understand that something happens during the cooling process, but cannot find any ...
Koushik Sarkar's user avatar
1 vote
1 answer
53 views

How accurate are float samples when looking for outcrops?

Near an old fire-trail I found a single fist-size igneous rock that I identified (as an amateur geologist) as belonging to a formation that is not known of in the area but is known to occur in the ...
Tom P's user avatar
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1 answer
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Mud cracks formation

Are mud cracks formed during rock formation or after the rock is completely formed?
Flora561's user avatar
1 vote
1 answer
75 views

Identifying dense magnetic rock with tubular features [closed]

I recently found a few rocks scattered in a valley, without any clues about where they may have come from (they did not look anything like the local soil, rocks, or layers of rock that could be seen ...
Massagran's user avatar
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2 answers
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Is there a theoretical maximum size limit for a rock?

There are many types of rocks: igneous rocks, sedimentary rocks, and metamorphic rocks. Some rocks are simply huge. Some of them are tiny. Is there a theoretical upper limit on the size of a rock, and ...
Arunabh Bhattacharya's user avatar
5 votes
2 answers
218 views

Why does calcium occur together with felsic rocks and magnesium with mafic rocks if calcium is denser than magnesium?

Felsic rocks contain a lot of sodium, potassium and calcium (and a great deal of aluminum), while mafic rocks consist of a lot of magnesium with iron.... Why is this? Why is magnesium (z=12) in the ...
Kurt Hikes's user avatar
2 votes
1 answer
181 views

Identify source of rings pattern in flint

This stone was found at the beach on the Danish side of Øresund (Amager strand in Copenhagen). I believe it is flint, though I am not sure. There is a pattern of rings on one of its sides (see photos)....
Osmor's user avatar
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Hexagonal phenocrysts with a metallic luster?

I recently realized that I am surrounded by interesting rocks. Having no background in geology nor geologist friends, I rely on online resources to navigate the intriguing stuff I stumble across. But ...
ben's user avatar
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3 votes
0 answers
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Are rocks extracted from deep drilling, brittle due to pore pressure?

When a saturated rock sample is rapidly extracted from a place with high water pressure, as happens in oil drilling or deep mining, the water is trapped inside the rock at high pressure, trying to ...
kefip's user avatar
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3 votes
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Why does the sandstone in Yehliu and other scenic coastal northern Taiwan look like vanilla fudge swirl ice cream?

I had the photos below handy from a recent trip, but in other areas of northern taiwan you can see very long, thin sheets of this dark, rust-like "chocolate swirl" separating very large, ...
uhoh's user avatar
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Are river rocks and stones a renewable resource?

Imagine the polished / unpolished rocks and stones that people use to decorate their homes and gardens. Are they a renewable resource? Are there plenty of them? If we give 200 pounds of them to each ...
Bear Bile Farming is Torture's user avatar
2 votes
1 answer
105 views

On QAPF (Steckeisen) diagrams, should Albite be considered on the Alkali feldspar or Plagioclase side? Or in-between?

QAPF diagrams are double ternary diagrams used for magmatic rock classification based on mineralogy. Quartz and Feldspathoids are opposed on the pointy ends of the diamond, with Alkali feldspar and ...
Hanatake Yurii's user avatar
1 vote
1 answer
551 views

Geology of the San Gabriel mountains in the Angeles national forest - rock types

I'm not a geologist, I am a hiker. And after many hikes in California's Sierra Nevada and Utah's red country I figured it would be great to learn some geology and I'm just posting this question to see ...
Amperie 's user avatar
3 votes
0 answers
56 views

Why does fracturing occur along a specific plane or region of the rock?

In this typical image of rock fracturing, why do the joints / fissures occur where they do, as opposed to, say, along the line drawn in blue on the image? More specifically, what characteristics of ...
charlie_sar's user avatar
4 votes
0 answers
159 views

Patterns on Basalt

These Basalt rocks were hand cracked and used to build the walls on my home. Many of these rocks have these semi circular pattern, made of the basalt itself. It's just a bit darker than the rest of ...
Delson Roche's user avatar
2 votes
1 answer
121 views

What is the "healthiest" rock?

When talking about rocks, i.e. an aggregate of minerals, which type would be the "healthiest" I'm not talking about some voodoo crystal-healing stuff here, just if there is any rock ...
xashm's user avatar
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1 vote
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793 views

Igneous and Sedimentary Rocks' Susceptibility to landslide

Which is more susceptible to landslide based on lithology compared to one another? Granite, Conglomerate, Sandstone, Mudstone I've been tasked to create a hazard map and was given a Geologic Map, ...
Account 1 Shlope's user avatar
4 votes
1 answer
70 views

Internal rocks in glaciers

I am very new to the study of the cryosphere. I was looking at the GLIMS inventory for glaciers and observed red patches as shown below which the legend mentions the red patches as internal rocks. In ...
user157522's user avatar
2 votes
1 answer
777 views

Looking for Rock/Mineral Identification Flowchart

As a christmas present, I bought a box of minerals/rocks for my girlfriend, who recently got interested in geology. Unfortunately, she could not attend the identification class in university. The box ...
infinitezero's user avatar
4 votes
2 answers
807 views

Why is felsic (granitic) lava so much more viscous when flowing (or trying to) than mafic (basaltic) lava?

A lower average temperature is, apparently, only part of the answer.... Several sites said composition, not temperature, explains most of the difference... And the difference in viscosity can be up to ...
Kurt Hikes's user avatar
5 votes
2 answers
256 views

Why is the inner core about 85% iron and the rest (mostly) nickel, while the outer is roughly 80%/20%, if nickel is denser than iron?

The question is basically the title. I really cannot think of a good reason. Is it a mystery to geologists?
Kurt Hikes's user avatar
0 votes
1 answer
164 views

Where to find graphite rocks? [closed]

Where to find graphite rocks? I made researches in my city beach but I don't know where to find them.
user24547's user avatar
1 vote
1 answer
110 views

What is the sedimentary form of gabbro/diabase? What would it look like?

Gabbro is an intrusive, mafic, and igneous rock. How would it turn into sedimentary rock?
Lulu M's user avatar
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4 votes
1 answer
563 views

Are there any rock recognition practices or games?

I'm a complete beginner in fossil collection but from my understanding I should mostly look at sedimentary rocks for fossils. However the problem is that rocks that I see in real life are not the same ...
Nicholas Humphrey's user avatar
1 vote
1 answer
110 views

How did these holes form in the rock? [closed]

I've been trying to figure out how these holes formed in the rock. These pictures were taken in Quebec, Canada on small lake in cottage country. The strange thing is that they are almost both ...
David A's user avatar
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2 votes
1 answer
152 views

Does water affect radiometric dating?

When radiometric dating, would water affect the measured age of old rocks ? Specifically would water affect Uranium-238 to Lead-206 dating of Zircon crystals? Would it affect the lead since it’s ...
Beans's user avatar
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3 votes
1 answer
125 views

Are we observing sedimentary rock formation today?

For instance, are we able to see the microscopic accumulation of shale or limestone? Can anyone reference me to sandstone formation observation, that would have to occur more rapidly. I’ve heard it ...
Colin Skinner's user avatar
3 votes
2 answers
374 views

What is this fossil found in flint in Kent?

My 7 year old son found this fossil whilst cracking open flint in Deal, Kent. The fossil (assuming it is) looks like scales/cells/shell and is chalky. The oblong lines are raised and well defined and ...
Andy's user avatar
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2 votes
0 answers
92 views

What kind of rock is this? [closed]

A few years ago in Venezuela, parque nacional de Cainama, the tourist guide found and gave me this rocks, he told us that a geologist told him that those could be radioactive but no one believed him. ...
PauC's user avatar
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3 votes
1 answer
512 views

How did this stone become encased within different rock?

My father, in his younger years, was a stone mason in Cincinnati Ohio. A couple of decades ago he was building a wall of some kind. He would fetch rock from a creek bed, haul it to the construction ...
Kenny's user avatar
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1 vote
0 answers
50 views

Prevalence of 'well-rounded' beach fabric on the Foreshore

Apologies for the vagueness of this query, but generally, would it be plausible to state that the prevalence of 'sub-rounded'* beach fabric is more common at the foreshore than 'sub-angular'* beach ...
Meteodeep's user avatar
3 votes
1 answer
165 views

How to identify chemical property and structure of rocks?

I am interested in identifying the properties of rocks. For example, black opal is shiny and can emit 5 different colors based on different lighting conditions. Is there a way for an amateur to be ...
I got vaccinated today's user avatar
2 votes
1 answer
64 views

Ore Deposit Identification

What type of ore deposit does this rock best represent? A rock with a porphyritic texture is cross cut by a stockwork of quartz veins. Bordering the veins is extensive alteration of the host rock. ...
Edward's user avatar
  • 55
4 votes
2 answers
122 views

Feldspar content of coarse-grained igneous rocks

From the chart, I would say that plagioclase feldspar is more abundant in coarse-grained igneous rocks than alkali feldspar, as it is found in all three listed, whereas alkali feldspar is only present ...
Jonathan's user avatar
  • 121
1 vote
1 answer
448 views

Arabian Desert rock formation

I'm interested about this rock formation in Arabian desert. The rock looks like melting chocolate. Not sure where the exact Location, the source says it around Al-Ula, Saudi Arabia. Here the image ...
user avatar
4 votes
4 answers
355 views

How is it possible for rocks to be trapped within another type of rock?

More specifically, I would like to know how the rocks in these pictures have formed: If this is because magma has melted and trapped the other rocks inside, do they have a different melting point ...
Marco Prins's user avatar
1 vote
1 answer
230 views

What causes dye to bleed from an agate stone?

I came across this review on Amazon. The cold drink was placed on top of the agate stone and the dye bled and left a permanent mark on the table. Why does this happen? Is it because of the ...
Mac_79's user avatar
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5 votes
0 answers
200 views

What's eating this sandstone

I decided to remove the tiles in my front courtyard and turn it into a garden of succulents. After removing a couple of rows of tiles then digging into the soil, I started seeing a strange thick ...
Fifi's user avatar
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4 votes
0 answers
158 views

How would one go about drawing the contour lines for this map in order to draw the cross section?

Good Day. We Received this map as practice for our Geology university module and I have no idea how to draw the strike lines where the different heights intersect the different rock types in order to ...
KaapseDwergie2020's user avatar
1 vote
0 answers
53 views

Lamé parameters of granite and similar rocks

I am looking for a book or an article where I can find the Lamé parameters of Granite, any help would be appreciated.
Tulip's user avatar
  • 111
1 vote
1 answer
478 views

What is this red glassy rock [closed]

I found rocks looking like this in my backyard but cant get to know what they are or how to find out. Below are pictures I don’t know if there’s more info I should mention. If there’s anything please ...
jaafar Nasrallah's user avatar
5 votes
3 answers
495 views

Why does radioactive dating work on specific rocks?

As I understand it, radioactive dating measures time by what portion of a radioactive isotope has decayed. Weren't all the natural radioactive isotopes created during the formation of the solar system?...
davidvgalbraith's user avatar
1 vote
0 answers
46 views

Megaspherulite growth

I have been fascinated by photos of these for a while, and I would like to ask how megaspherulites grow so large, when spherulites are normally quite small? I also noticed that all papers about the ...
DanPar's user avatar
  • 111
3 votes
2 answers
189 views

Why aren't there ultra acid igneous rocks?

In my study, I found that in volcanoes when the magma is going up it formed different types of rocks. There are basic, acidic and ultrabasic. My question is why isn't there ultra acid igneous rocks ...
user272506's user avatar
2 votes
3 answers
166 views

Using Enhanced Rock Weathering in the Sahel Region of Africa

A recent Guardian article "Spreading rock dust on fields could remove vast amounts of CO2 from air" has gotten some attention in the nongovernmental and UN organizations working in the Sahel ...
Eric's user avatar
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