Geology

Do you ever wonder why one river is straight and flows quickly while another meanders along curves and seems to be slow and peaceful, or how the mountains were formed? Geology is the study of the earth, its materials, and the processes acting upon them. It includes the study of rocks and minerals; and their formation, weathering, and metamorphosis. So, when you need an answer to a question about rivers, mountains, volcanoes, rock cycles, plate tectonics, or other geological aspects, our Geology category is the place to ask it.

94,525 Questions
Geology

Can apatite scratch glass?

Probably not as apatite has a Mohs hardness of 5.0 and window glass lies between 5.0-6.0 on the Mohs scale. A higher Mohs number cannot be scratched by a lower number.

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Geology
The Difference Between
Rocks and Minerals

What is the difference between a rock and a mineral?

A rock is formed from minerals; a mineral may be considered as a chemical compoud with a chemical formula. The rock is a mixture.

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Geology
Erosion and Weathering

What are the differences between weathering and erosion?

Weathering is the breaking down of rock into smaller and smaller particles. Weathering processes include frost wedging, acid rain dissolution, root growth, wind particle abrasion, heat expansion cracking, hydraulic fracture, and rock tumbling in rivers and streams.

Erosion is the movement of weathered material from one place to another place through the agents of erosion: wind, water, ice, and gravity.


In tandem, weathering and erosion act to lower the high points, and raise the low points on the surface of the planet.

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Geology
Mountains
Valleys

How are mountains formed?

Volcanic mountains are formed either through the introduction and accumulation of magma over a crustal "hot spot" or through volcanic activity associated with the collision and subduction of a crustal plate, where the melting of the subducted crust creates magma, gases and pressures that are released in eruptions.

Continental crustal plate collisions, where neither plate subducts, create mountain ranges such as The Himalayan Mountain Range, where crustal material is thrust upward faster than erosion can wear it down.

Plates can stretch until they crack and slide, forming fault-block mountains.

In the ocean, great underwater mountains are formed when plates spread away from one another, and melted rock pushes up through the gap, creating hot, buoyant elevations of new crust (a simplification of the process).
Many mountains inclueding Everest were created by two of Earths tectonic plates pushing against each other.

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Geology
Paleontology
Fossils

How do you determine the age of a sedimentary rock or a fossil contained within it?

This an area of common misconception. Most sedimentary rock, and the fossils contained therein cannot be dated directly with radiometric techniques, but can be dated indirectly. Here's the facts:

  • Because most sedimentary rock is composed of particles of pre-existing rock of various types, each particle can be a different age.
  • Carbon-14 or carbon dating techniques can only be used to date organic material which is of a maximum age of 70,000 years; this leaves out the vast majority of fossils found in rock, and only covering roughly .000016 percent of geologic time.
  • The dating of fossils was originally done by their placement in a geologic column of rock strata. Because of the Law of Superposition, the deeper the stratum, the older it is (in an undisturbed body of rock or sediment). Fossils which were evident in a particular stratum, but missing from other strata were noted as "index" fossils. The presence of these fossils indicated the age of the stratum relative to other layers. The layers of stratum were placed in a geologic column, subdivided, and assigned names based on the presence of different types of fossil organisms. The use of fossils in this manner is known as biostratigraphy and is the basis of "relative dating" of rock layers and fossils, a dating technique that was in effect until the advent of radiometric techniques in the twentieth century.
  • Radiometric dating of rock involves the measurement of the amount of decay in radioactive elements which are present in the rock. Radioactive elements decay at unique rates, depending on the isotope. This rate of decay is known as half-lives, it is the time necessary for ½ of the atoms to decay in a particular element. The decay follows a geometric scale, in that in the first half-life of an element, ½ of the atoms decay, yet in the second half-life, ½ of those remaining decay and so forth. By measuring this decay, and knowing the half life of an element, scientists can date a sample. Radiometric dating is particularly useful in dating igneous and metamorphic rock.
  • Because of geologic events such as plate tectonics and volcanism, suitable material for radiometric dating, such as volcanic tuff, solidified lava, and igneous intrusions have been found as layers on, in, and cut through layers of sedimentary rock. Intrusions are always younger than the rock body they penetrate, meaning that the sedimentary rock in which intrusions are found will be older than a radiometrically dated sample of the intrusion. Lava flows and volcanic ash which form layers in rock will be younger than the rock below and older than the rock above. The solidified intrusions and lava flows can be dated with radiometric techniques.
  • The radiometric dating of suitable rocks (i.e. igneous or metamorphic) in proximity to their sedimentary counterparts, therefore allows the sedimentary rock to be dated as well.
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Geology

What are two ways a mineral can form?

A mineral can form when molten material solidifies, or when a saturated solution evaporates.

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Geology
Social Sciences

How does sandstone rock feel?

Sandstone feels rough, much like sandpaper.

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Science
Geology
Planetary Science

How do crater counts tell us the age of a surface?

The more craters a surface in space has (e.g. moon's surface), the older it is likely to be. A surface which has been around longer will have been exposed to more impacts from objects such as meteorites.

In addition, if you are able to get figures for the rate of crater production, it is possible to use the number of craters to give an quantitative estimate of the age of the surface.

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Geology
Plate Tectonics

How far apart are tectonic plates moving?

The tectonic plates move at about the same speed your finger nails grow. The gap the plates create when they move apart is constantly being closed up by magma moving up from the mantle.

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Hobbies & Collectibles
Geology
Agates

Where can you find moss agate buyers?

you can find them in montana

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Geology
Rocks and Minerals

6 methods to tell minerals apart?

Six methods to tell minerals apart?

1) Acid test = will it bubble? is there a light, strong, or no reaction to the acid 2) color= white, black, green, pink, or gold 3) streak= black. Brown. White. Red. This tests the powder color of the mineral 4) luster= dull, pearly, shiny 5) weight = gravity test 6) hardness= this is a scratch test mineral against a penny and a file.

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Geology
Food Safety

Is silica safe to eat?

Why would you want to??? Probably nottt!!!

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Geology
Earth Sciences
Forests

What is the difference between mineral and forest wealth?

mineral is found below the earth while forest is above the earth

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Geology
Countries, States, and Cities
International Business and Trade

What country has the world largest gold reserves?

The USA by far.

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Geology
Chemistry
Mining

Is Bauxite a iron ore?

it's an ore of aluminum. Bauxite is a rock composed of aluminum oxide minerals. It is found at or near the Earth's surface.

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Geology
California
Rockhounding and Mineral Collecting

Where do you find geodes in California?

The Hauser Geode Beds, SW of Blythe, offer good geode collecting in several different areas. For further details, it's best to join a local gem and mineral club, consult your state geology department, or a local university or museum's earth science department.

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Geology
Jewelry
Chemistry
Elements and Compounds

What elements do alexandrite contain?

Alexandrite is the highly regarded color changing variety of Chrysoberyl. The color of Alexandrite changes under different lighting conditions. If viewed in daylight, its color is greenish blue to dark yellow-green. If viewed in incandescent or candle light, its color is pink to red. Its chemical formula is BeAl2O4, it has a hardness of 8.5 on the Mohs scale and a refractive index of 1.744 - 1.755. Source: http://www.minerals.net/gemstone/alexandrite_gemstone.aspx

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Geology
Earth Sciences
Earthquakes

What is the function an earthquake?

Earth has lots more earth quakes than it use too. These increases started after different countries took up experimenting and Blowing up giant Bombs deep in the Earth! The Atom and Nuclear Bombs the hardest and causing the most damage in quakes.

I wonder what God this of our doing these?

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Geology
Gold and Precious Metals

How much does rhodium cost per ounce?

As of today (27th July 2012) its 1275 $/ounce (31.1 grams).

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Geology

What is mineralogy and what does a minerologist do?

mineralogy is the study of minerals and a minerologist specifically studies minerals there chemistry, molecular bonds, miller indices, and assorted specific features of minerals.

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Geology
Rocks and Minerals

Is limestone the hardest rock?

No, far from it. Limestone is actually quite soft, rating only a 3 or 4 on the Mohs scale.

Care should be taken when making generalisations about rock properties.

Hardness is a function of a material's elastic modulus (how much it deforms under a given load).

Limestone (like all rocks) is a natural Earth material. As such it can display a very large variability in properties.

For example limestones can have Young's modulus values ranging from 9 to 70 MPa.[A] This is clearly very variable, but the upper bound values are comparable with values derived for "hard" rocks such as metamorphic hornfels and the coarser grained igneous rocks such as granite, whereas the lower bound values are very soft indeed by rock standards.

So to answer the question, no, limestone is not the hardest rock, however some types of limestone can be classed with some of the hardest rocks, whereas other types may be some of the softest.

[A] Bell, F. G. (2007). Basic Environmental and Engineering Geology. Dunbeath, Whittles Publishing Limited.

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Geology
History

Where are the oldest rocks in the atlantic ocean found?

The Atlantic Ocean started to form about 200 million years ago, shortly after the beginning of extensive volcanic activity, associated with tensions in the continental crust between nowaday's Afrika and North America. The oldest oceanic crust in the Atlantic Ocean is therefore found off the continental slopes of the USA and Northwest Africa.

The continental shelfs, of course, comprise rocks below their sedimentary cover that often are much older than the oldest oceanic crust.

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Geology
Chemistry
Mining

What are the uses of limestone?

Limestone Uses:
  1. Used as aggregate or base for roads and foundations.
  2. Used in the purification of molten glass.
  3. Used to remove impurities from molten iron.
  4. Used as filler and abrasive in toothpastes.
  5. Used in the production of Portland cement.
  6. Used as an aggregate in concrete.
  7. Used as a soil conditioner for neutralizing acidic soils.
  8. Used as a source of calcium in supplements and food additives.
  9. Used to make paper white.
  10. Used in the purification of sugar.
  11. Used in the manufacture of brake pads.
  12. Used in the manufacture of medicinal antacids.
  13. Used in the preparation of wools and dyes.
  14. Used as a construction stone in buildings.
  15. Used as counter tops and flooring.
  16. Used as a water neutralizer.
  17. Used as a paint additive.
  18. Used as landscaping rock.
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Science
Geology
Earth Sciences

Is sand carried as far as gravel?

sand is carried farther than gravel because it weighs less and doesn't get stuck together.

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Technology
Geology
Earth Sciences

What are windows to earths interior?

Mantle-derived xenoliths.

The magma is mantle and/or subducted-crust-derived.

Xenoliths come from the country rock through which the magma rises, so really it's the magma (solidifying as igneous rock) that's the window.

For greater depths, seismic analysis is the window.

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