Questions tagged [rocks]

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

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19
votes
4answers
17k 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 ...
16
votes
2answers
60k views

Are the processes of the rock cycle currently in dynamic equilibrium?

The standard representation of the rock cycle usually looks like this: Does each stage of the rock cycle currently balance? That is, are the various processes in dynamic equilibrium, so that the ...
14
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2answers
927 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 ...
14
votes
1answer
230 views

How are the patterns in solid rock born

I took this photo on my vacation in Finland showing white stripes in the rock going different ways. How are these patterns born?
13
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1answer
9k views

How are giant sinkholes filled up?

There are a few impressive photographs of giant sinkholes that appeared in cities, such as this one: However, followup information (e.g. Guatemalan sinkhole) or photographs on how these kind of ...
13
votes
1answer
546 views

Formation of limestone without living organisms?

Limestones are formed mostly from skeletal fragments of marine organisms. However, calcium carbonate dissolves naturally in water, so the living organisms are not the only source of it in water. Is ...
12
votes
1answer
585 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 ...
12
votes
0answers
451 views

What is the global distribution of oil filled geodes?

In a general 40 mile radius of Keokuk, Iowa many sedimentary geodes can be found. They are abundant in the Warsaw Formation with the type section at Geode Glenn in Warsaw, Illinois. In one specific ...
11
votes
2answers
20k 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 ...
11
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2answers
3k views

Zeolites, odor control, and the witchcraft of sunlight

Various companies offer "volcanic crystals" or "volcanic rock" available in small mesh bags for odor control. The best description I have found is that these are made up largely of Zeolites. All of ...
11
votes
2answers
295 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 ...
11
votes
3answers
1k views

Identifying sedimentary rocks in hand specimen

I'm currently learning how to identify rocks in hand specimen. The initial classification into igneous, metamorphic, and sedimentary is mostly ok, but I'm having a problem with further identifying ...
11
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3answers
4k views

What is the oldest sediment?

Sedimentary rocks in Akilia or at Hudson Bay have been proposed as the oldest in the world. My question is not related to rocks, but rather to sediment while still forming sedimentary deposits but ...
9
votes
3answers
713 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 ...
7
votes
4answers
1k views

How is this crumbly crystal-rich rock formed?

I found this crumbly rock embedded in the channel walls of a small creek in Everett, WA, USA. (North Creek that flows through McCollum Park.) If possible, I'd like to know how the rock formed... what ...
7
votes
2answers
573 views

Non-invasive techniques to find rock composition

If we had access to a totally new kind of rock (maybe a new meteorite), is it possible to tell what the rock is composed of without touching it / drilling into it? I'm thinking of something like ...
7
votes
3answers
408 views

Could one say that granites are metamorphic rocks, or not at all?

In my old textbooks, granites used to be part of the metamorphic rocks. Is this still true or not ? If not fully true, to which extent ? Could someone point me towards clear examples or definitions ...
7
votes
3answers
352 views

Is there a widely accepted reason for the formation of tafoni?

Expansion of tafoni seems to be based on weathering (seems reasonable enough.) But what creates them in the first place? There are a number of explanations online (Wikipedia lists eight plausible ...
7
votes
2answers
187 views

Recreating the rock cycle

I want to recreate the rock cycle using some item that can behave as a rock. The purpose of this is to get a point across to my students about how really there is a reason why the rock cycle is called ...
6
votes
1answer
916 views

How can a non-geologist identify a rock? [closed]

I found a rock on a beach in north-east Evia, Greece. Half is light gray, and half is dark gray. There are white (or very light gray) thin lines that form swirls throughout, crossing the light/dark ...
6
votes
2answers
83 views

Curious natural patterns on the surface of basalt blocks that make up the sidewalk

During one of my walks through the city streets, I noticed that some basalt blocks that make up the sidewalk have in their surface some very curious natural patterns: The photos above was taken at ...
6
votes
4answers
7k 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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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?
6
votes
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
votes
0answers
171 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 ...
5
votes
3answers
77 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?...
5
votes
3answers
273 views

Making a local geological field trip an interesting and educational event for children?

I have no expertise in geology or earth science, but I would like to do a "field trip" with my home-schooled young children (under age 10) where I could teach them about geology from a hands-on ...
5
votes
1answer
296 views

Spatial Continuity in python

I have data like this of rocks from 3 blast holes: These are the rock properties of each blast hole of a mining site. The rock properties come from the Block model of that mining site. I want to ...
5
votes
1answer
116 views

There are cloud identification guides, are there also (guided) rock identification websites?

Seeing all these rock identification questions, got me wondering, is there no straightforward guided rock identification website? In Intro to Geology lab, I remember going through a bit of a process ...
5
votes
1answer
135 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 ...
5
votes
1answer
180 views

Identification of limestone type

These are images of a stone found and used extensively in the Jammu & Kashmir region between India and Pakistan. These are called devir or devri in the local parlance. Following is the ...
5
votes
4answers
81 views

Sources or strategies for stone identification

I have a bunch of semi-precious stones here, but I am not very learned in geology etc and I would like to have some way to know what kind of stones they are. As far as I understand question about ...
5
votes
1answer
210 views

Why would CaO be more finely spread than K2O in Granodiorite?

I recently interpreted some XRF data on samples of a granodiorite which were classified under three different types of physical characteristics: very little, mild and significant levels of weathering. ...
5
votes
1answer
242 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 ...
4
votes
2answers
953 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 ...
4
votes
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 ...
4
votes
1answer
495 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?
4
votes
1answer
2k 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 ...
4
votes
1answer
185 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....
4
votes
0answers
688 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
votes
2answers
180 views

Why are metals so separated in the Earths crust? [duplicate]

I find it very surprising that metal ore deposits are so separate, and unevenly separated on the Earth. I do understand that there were various different conditions at some point in time in the ...
3
votes
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 ...
3
votes
2answers
1k views

Radon is a naturally occurring radioactive gas. How does this work?

Radioactive rocks can release a gas called radon when they decay, which can build up in the basements of buildings with serious effects on people's health. Does anybody have information on how radon ...
3
votes
2answers
109 views

Odd Inuksuk-like objects

I found some huge objects that are way too big to be inuksuks, in my opinion. The object on the right is very odd because the arms are not straight like they are in most images of inuksuks. and ...
3
votes
2answers
449 views

I found this strange spherical stone in Gillette Wyoming. I have no idea what it is. Please help. [closed]

These are recent pictures of it. It’s heavy, I see small minerals that catch the light in it, very bumpy, spherical, doesn’t seem to be magnetic, I was falling down a deep trench and kicked it up at ...
3
votes
2answers
526 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 ...
3
votes
2answers
274 views

A few questions about glass

A glass, as I understand it, is a material whose solid phase is amorphous and which undergoes a glass transition when heated. My train of thought - and therefore my questions - began with obsidian. ...
3
votes
1answer
2k views

What's the difference between cleavage and fracture?

I see both terms refereing to fractures on crystals or minerals, so I wonder if they could be considered synonymous. If no, what's the difference between both terms?
3
votes
1answer
1k views

What is the difference between subvolcanic rocks and plutonic rocks?

I'm studying Plutonic (Intrusive) rocks and I really don't understand the difference between Plutonic Rocks that form in Sills and Dikes from the so called subvolcanic rocks, also known as a ...
3
votes
5answers
961 views

Where are the oldest igneous rocks found?

I'm trying to catch up on my homework for earth science, but I'm having a difficult time searching for an answer to my question.