28 votes

Where can obsidian be found?

The processes forming obsidian are not well understood because an active obsidian-forming eruption has never been recorded by humans. However, we can make many inferences from the composition of the ...
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  • 2,563
20 votes
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Why do gold deposits form only in certain areas of the earth?

I'll take the form of the question given by another person here and attempt to provide a different answer. So what you are asking is: "How did gold become so concentrated in certain parts of the ...
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19 votes
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How do geologists find ore deposits?

That is the multimillion dollar question! "looking for surface formations" is indeed one way, and it was the main method of exploration in the past. This does not necessarily mean that you directly ...
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  • 22.2k
19 votes
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Can ultrasounds be used to map the density of large underground regions?

Sound-like waves are routinely used to image the subsurface, but mostly well below the ultra-sound band. Several methods involve sound-like vibrations: Reflection seismic — the most important ...
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18 votes
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Where can obsidian be found?

Obsidian is formed when a rhyolitic (or felsic) lava flows cool rapidly. This must mean that it's mostly available on the surface (and I think if you go near volcanos you can find pieces of Obsidian ...
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  • 6,376
18 votes
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Why do felsic materials have lower melting points than mafic?

I'd like to add to Brian's answer, and also point out some inaccuracies. First of all, it is not true that felsic minerals have lower melting temperatures than mafic minerals. Here are some melting ...
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  • 22.2k
18 votes
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Why would India have so much thorium on its beaches?

why would India have so much thorium on it's beaches...? Because monazite. Monazite is a rare earth element phosphate, with the formula CePO4 (where Ce stands not only for cerium, but all of the are ...
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16 votes
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What are the implications of the recent discovery that huge oceans exist close to the mantle of the Earth?

I am going to assume that you are referring to recent new stories with titles like "Rare Diamond Confirms That Earth's Mantle Holds an Ocean's Worth of Water" (Scientific America). These articles are ...
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  • 541
13 votes

Why are minerals found in "large" quantities and not scattered throughout the earth as individual atoms?

First of all, Earth is not a random assortment of atoms. While it probably formed along like that in the beginning, somewhere along the way it differentiated into distinct core, mantle and crust, ...
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  • 22.2k
13 votes

How do geologists find ore deposits?

In addition to the above, what happens is that people look for commonalities between known deposits. So, for example, if you have a lot of gold veins in one area, and lots in another area, then you ...
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  • 441
12 votes

Where can obsidian be found?

I have seen it on the surface in some the lava fields of Iceland. This is consistent with @Neo answer. Obsidian is not that often present, but if present, there is usually plenty around. It occurs in ...
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  • 516
11 votes
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How do you use the streckeisen (QAPF) classification ternary diagram to identify igneous rocks based on chemical rock composition?

Why you should not do it The QAPF and related diagrams are intended for classification of rocks in the field, or preliminary classification with modal proportions as seen in the optical microscope. ...
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  • 22.2k
11 votes
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What are the high field strength and large ion lithophile (HFS or HFSE & LIL or LILE) elements?

First, a short introduction to incompatible elements The Earth's mantle is mostly composed of the minerals olivine, pyroxene, anorthite, spinel and garnet. These minerals are made from the elements ...
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  • 22.2k
11 votes

How do geologists find ore deposits?

I've been looking for these things over a few decades and along with other geologists doing this we have seen how we find things change somewhat. Many methods used a century ago are still in use, but ...
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  • 425
10 votes

Are there minerals which are not been found on earth but which are still possible to exist?

To answer the first part, there are many minerals on earth which do not involve silicate bonded structures. For instance, non-silicates (minerals of carbonates, sulfides, sulfates, phosphates, and ...
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  • 101
9 votes

Connection between microbes and serpentinite?

The most common explanation for microbial activity in serpentinites is the exploitation of abiogentic hydrogen and methane formed during the serpentinisation process. Quoting the abstract of a recent ...
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9 votes

What is the geologic origin of Cryolite, and could there be more?

Ivigtut Cryolite deposit, Ivittuut (Ivigtut), Arsuk Fjord, Sermersooq, Greenland deposit is the first and largest occurrence of Cryolite but it is not the only location to report Cryolite. Some of ...
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9 votes

Are there any areas on Earth with purplish-colored soil/sand/rock/land?

Soil color is highly dependant on the oxides and other minerals in the composition. Purplish tones appear to be possible by inclusion of manganese oxide compounds. There are locations in China that ...
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9 votes

Are there probably decent oil fields located in the middle of the ocean?

Are there probably decent oil fields located in the middle of the ocean? tl;dr: no. Hydrocarbon deposits form by thermal maturation (i.e. slow and mild heating) of buried organic matter (i.e. dead ...
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9 votes
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What are the cubic formations found inside Larimar gemstones?

Calcite and hematite may not be the the answer to my question Hematite is not the answer, but calcite is. The inclusions are not cubic, they are rhombohedral. This is precisely how calcite looks ...
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8 votes
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Why are titanium oxides lumped in with magnetite for the purposes of analyzing water bubble nucleation?

In iron oxides, titanium commonly substitutes for iron in the crystal structure. Two solid solution series are important: the ulvöspinel-magnetite and ilmenite-hematite series. The composition of a ...
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8 votes
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In what sense did the Oklo reactor "trap" its own nuclear waste?

According to Record of Cycling Operation of the Natural Nuclear Reactor in the Oklo/Okelobondo Area in Gabon, the Xe is trapped in crystalline cage-like structures formed of the aluminum phosphate ...
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  • 5,912
8 votes
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Where can fluorite be found on Long Island, New York?

I do not know of fluorite being reported to occur on Long Island. If fluorite is found in NYC, the Natural History museum might have specimens. You might try contacting a mineralogy / mineral ...
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8 votes

Which Earth minerals would Moon colonists miss the most?

The composition of Moon rocks is pretty much the same as that of Earth. However, none of the processes that concentrate specific minerals in one location (i.e. into a mineral deposit useful for mining)...
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8 votes

What kind of purple stone is this?

That's amethyst, a violet version of quartz See here
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  • 744
7 votes

How are spherulitic structures formed in basalt rock?

According to the image that you provided, what you are seeing are not spherulites, but rather epoxy bubbles. More on that later. I will first answer what are spherulites: Spherical features observed ...
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