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
votes
1answer
580 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
votes
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
653 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 ...
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2answers
518 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
382 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
789 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
219 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
648 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
votes
1answer
445 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, ...
11
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4answers
3k views

What sort of rock is the large polished boulder? [closed]

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?
14
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2answers
889 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 ...
5
votes
1answer
219 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 ...
11
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2answers
290 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 ...
6
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1answer
548 views

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

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
743 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
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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 ...
19
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4answers
15k 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 ...
3
votes
1answer
110 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 ...
7
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2answers
174 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 ...
5
votes
1answer
804 views

What type of sparking stone could this be? [closed]

A few years ago, I went to a beach in the south part of Chile, specifically Lake Lanalhue, it was filled with special rocks that when you picked one up and threw it against another that you would see ...
11
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2answers
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 ...
11
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2answers
2k 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 ...
14
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1answer
224 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?
10
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1answer
829 views

What kind of coal did I find? [closed]

I found a piece of (what I believe is) coal, on Cape Cod last week. Its density is 1.43 grams per milliliter. With this information is it possible to know whether it's Anthracite, Bituminous or ...
12
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1answer
486 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 ...
11
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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 ...
16
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2answers
48k 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 ...
6
votes
1answer
905 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 ...