19
votes
Why is basalt denser than granite?
Magmas have a wide range of chemical (and mineralogical) compositions. Basalts come from mafic magmas (they used to be called "basic" magmas), while granites come from felsic magmas (used to ...
- 7,729
14
votes
Accepted
How are giant sinkholes filled up?
How Japan Filled That Ginormous Sinkhole In Just One Week:
The Fukuoka sinkhole measuring 8,700 square feet (808 square meter), 65 foot (20 m) deep: they poured a mixture of soil, water, and cement ...
- 2,679
13
votes
How long does it take for a stone to alter?
Mountains and rock do decompose or weather into sediment. A basic rock cycle overview shows the possible pathways between all three rock types (igneous, metamorphic, and sedimentary) how one type ...
- 5,959
13
votes
Accepted
Are "monoliths" giant, isolated rocks sitting in dirt, or are they continuous with bedrock
the trick is not all isolated rocks are produced the same ways. Of the two in your pictures the first is an old volcanic events; intrusions, dikes, ect. depending on which rock in the region you are ...
- 6,878
12
votes
Could one say that granites are metamorphic rocks, or not at all?
This is the key:
used to be part
It is important to look at this in a historical context. Up until the 1950s and early 1960s, there was no agreement to how granites form. This became the granite ...
- 23.1k
11
votes
Accepted
Non-invasive techniques to find rock composition
You are looking for a portable XRF.
It does (almost) exactly what you said. It sends electromagnetic radiation to the rock (X-rays), which excites electrons in the atoms and when they bounce back ...
- 23.1k
9
votes
What is this fossil found in flint in Kent?
That is a sea urchin (echinoid) or at least part of one. the pattern of plates is fairly distinctive. 2 rows of small plates alternating with 2 rows of large plates. I am not familiar enough with ...
- 6,878
8
votes
Accepted
What do you call boulders of non sedimentary rock that were lithified into sandstone?
The technical term for a sedimentary rock that has a lithified fine-grained sediment with larger pieces of rocks suspended in it upon lithification is a conglomerate. The fine-grained interstitial ...
- 518
8
votes
Accepted
Odd Inuksuk-like objects
I can engage in some educated speculation about what you think you see, but I'm confident you were fooled by the shadows in the image, which are caused by a low sun angle and distorted by the terrain. ...
- 3,548
8
votes
Accepted
How is this crumbly crystal-rich rock formed?
Even rocks that have lasted for billions of years decompose when exposed to Earth's weather.
What you have is indeed granite, but a somewhat decomposed granite, which is treated by geologists ...
- 3,548
7
votes
How are natural specimens, such as ‘Moqui Marbles’, distinguished from man-made artifacts?
Like Michael, I find your question a little unclear, but the crux of it seems to be this:
... does science have to conclude [that a specimen is] just a rock because the composition is entirely from ...
- 5,431
7
votes
How is this crumbly crystal-rich rock formed?
Yes, this is a granite.
It's hard to know exactly which one. A geological map of the area shows the bedrock to be sedimentary rocks, so this piece of granite was transported in the creek from far ...
- 23.1k
7
votes
7
votes
Accepted
Curious natural patterns on the surface of basalt blocks that make up the sidewalk
These are most likely manganese dendrites. It is not a fossil, and not organic. These usually form in cracks in rocks, and most likely this slab was broken along an existing crack.
You can read more ...
- 23.1k
7
votes
Are we observing sedimentary rock formation today?
The transformation of sand into sandstone per se cannot be directly witnessed, as it's happening deep in the earth. However, there are types of cementation that happen quickly and in plain view:
A ...
- 3,548
7
votes
Why is felsic (granitic) lava so much more viscous when flowing (or trying to) than mafic (basaltic) lava?
Several sites said composition, not temperature, explains most of the
difference...
They are correct. All other factors remaining equal, felsic magmas are more viscous. This is the result of higher ...
- 23.1k
6
votes
How to learn the different types of rock
Go to a good geological museum and spend time there. Alas, many
such museums have dumbed down, and are not as informative as they
used to be (Natural History Museum in Kensington, London - I'm
writing ...
- 14.2k
6
votes
Why is coal classified as a sedimentary rock?
I'm not sure why you are including shale in your question, unless you are referring to carbonaceous shale, which in not coal, but shale with carbon throughout the matrix of the shale.
Shale is an ...
- 24.6k
6
votes
How are natural specimens, such as ‘Moqui Marbles’, distinguished from man-made artifacts?
It's not completely clear what you're trying to ask here, but I'll have a go at it anyway.
If earth only had them would science say there are ancient artifacts from a past civilization?
The only ...
- 23.1k
6
votes
A human foot impression on a rock
As @kwinkunks and @Gordon Stanger say, it's not possible to comment usefully on your particular observation without at least a picture and further information about the site. However, if you're asking ...
- 402
6
votes
When metamorphic rocks undergo pressure, how are they changed?
Metamorphic rocks are formed when a rock (sedimentary, igneous or a previous metamorphic rock) comes under high pressure and/or temperature. Pressure and temperature forces the atoms to form new ...
- 5,936
6
votes
There are cloud identification guides, are there also (guided) rock identification websites?
I looked through your step-by-step cloud identification guides, and they seem pretty easy. The overwhelming criterion for which cloud it is is "how does it look", with the addition of the obvious "is ...
- 23.1k
6
votes
Where are the oldest igneous rocks found?
Zircons from Australia at 4.4Ga, and perhaps basalts from a Canadian island at 4.5Ga.
It would interest you to know the quest of Boston University geochemist Matthew Jackson, who is searching for the ...
- 1,339
6
votes
Accepted
Radon is a naturally occurring radioactive gas. How does this work?
Radon (more specifically Radon-222) is produced in the decay chain of Uranium-238. Radon-223 is also produced by the decay chain of Uranium-235 and Radon-220 is produced by the decay chain of ...
- 5,847
6
votes
How is it possible for rocks to be trapped within another type of rock?
There are three major types of geological formations that contain or are composed of various rocks:
breccia
conglomerate
xenoliths
Breccia
The word breccia comes from the Italian word for rubble. ...
- 24.6k
6
votes
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?
Once you're in the metallic part of the Earth, the compositions of the different constituents (solid and liquid) are not determined by density.
The whole metallic part (core) is denser the the ...
- 23.1k
6
votes
Identify source of rings pattern in flint
What you're looking at is a conchoidal fracture. It means you are looking at one half of a larger piece of flint. The strike that broke it occurred on the centre of the radial pattern, and it ...
- 23.1k
5
votes
Accepted
Was there once a glacier over Starcke national park in Queensland Australia?
That region forms part of the North Australian Craton and the underlying bedrock is in the order of 1.8 billion years old. The bedrock appears to be overlain by the Isa Superbasin during a period of ...
- 176
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