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20 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 ...
Jean-Marie Prival's user avatar
14 votes
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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 ...
Jan Doggen's user avatar
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13 votes
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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 ...
John's user avatar
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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 ...
Earth Science Expatriate's user avatar
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 ...
Gimelist's user avatar
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11 votes
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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 ...
Gimelist's user avatar
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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 ...
John's user avatar
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8 votes
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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. ...
Spencer's user avatar
  • 3,588
8 votes
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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 ...
Spencer's user avatar
  • 3,588
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 ...
Gimelist's user avatar
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7 votes

What kind of purple stone is this?

That's amethyst, a violet version of quartz See here
JulPal's user avatar
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7 votes
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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 ...
Gimelist's user avatar
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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 ...
Spencer's user avatar
  • 3,588
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 ...
Gimelist's user avatar
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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 ...
user2821's user avatar
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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 ...
Gimelist's user avatar
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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 ...
bandybabboon's user avatar
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6 votes
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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 ...
userLTK's user avatar
  • 5,857
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. ...
Fred's user avatar
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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 ...
Gimelist's user avatar
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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 ...
Gimelist's user avatar
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5 votes
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If rocks are stones, what type of rock are gallstones?

The nature of this question is more about biological chemistry than it is about earth science. This is because gall stones have nothing to do with geology, but chemical processes in the body. ...
Fred's user avatar
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5 votes
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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 ...
norman_h's user avatar
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5 votes
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What is this Lake Michigan rock?

I can't be definite but my three best guesses are Travertine, Agate and maybe Halite, if it fizzes in mild acid it's Travertine, a form of Limestone, if it dissolves in hot water it's Halite, or ...
Ash's user avatar
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5 votes

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

Radon, occurs naturally as an intermediate step in the normal radioactive decay chains through which thorium and uranium slowly decay into lead; radon itself is a decay product of radium. Some ...
Fred's user avatar
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5 votes

What is meant by intraplate volcanism?

Terms: Intraplate volcanism - as the name suggests it is volcanism within the plates rather than at plate boundaries. These are also known as hotspots. Ocean island basalt (OIB) - is the basaltic ...
shul's user avatar
  • 133
5 votes
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What is meant by intraplate volcanism?

The majority of Earth's volcanoes occur in plate boundaries. These can be at spreading ridges (green dots on the map) where they are mostly underwater, but sometimes are above the water (such as in ...
Gimelist's user avatar
  • 23.1k
5 votes

Spatial Continuity in python

Your last question was easy to answer, this one is more difficult. You could look at correlation and dependence, but you'd be better off looking at variography. That's the easier part of this question ...
Fred's user avatar
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