# Tag Info

## Hot answers tagged mineralogy

19

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 subsurface remote sensing tool we have Refraction seismic — important, but niche, and has a lot in common with reflection Acoustic logging — uses ultrasound, which ...

17

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 temperatures of common minerals, sorted from high to low: Forsterite (mafic): 1890 °C Quartz (felsic): 1713 °C Anorthite (felsic): 1553 °C Diopside (mafic): 1391 ...

17

Good question! As you know, Bowen's reaction series describes the order of crystallization of silicate minerals in a cooling magma. The complex anion of silicates is a tetrahedron of four oxygen atoms surrounding one silicon atom, connected with strong covalent bonds. Each tetrahedron may be isolated from one another or they may be bonded together ...

16

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 referring to research published in Nature: Pearson, D. G. et al. (2014). The researchers found an inclusion of ringwoodite inside a diamond. Here is a quote ...

15

I think Azzie's answer describes the situations where gold is formed and found as Lode deposits. But native gold in lode can then be subject to weathering when it is exposed, which releases the gold into the environment as flakes, grains and nuggets. This gold is then subject to erosive and sedimentary processes. As gold is denser than most minerals it can ...

14

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 world?" So yes, gold is all around but the concentration is too low to make extraction of it worthwhile. You need some process to take small amounts of gold from a ...

13

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 earth elements and yttrium as well). It is one of the main ore minerals for the rare earths. It's a very common mineral in granites and similar rocks, and it's ...

12

The hardness of minerals is diagnostic because the hardness is determined by the strength of bonds and the structure of the mineral lattice. Hardness is basically the stress required to create and grow extended lattice defects such as micro-fractures, stress twins, and dislocations. Diamond, quartz, and framework silicates, such as feldspar, are hard ...

12

It is bond strength, not hardness, that determines how easily oxygen can attack and burn a material, allowing me to burn a diamond in a pool of liquid oxygen resting in a block of graphite. Diamond is hard because its bonds form an inflexible, three-dimensional lattice. However, the strength of these bonds themselves is not even as strong as graphite, ...

11

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. They are not designed with the chemical composition of the rocks in the mind. Furthermore, these diagrams are merely descriptive and not genetic. They do not ...

11

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, which are not chemically the same. That's a story for another question though, and there is an excellent answer to it on this site. Back to your question, Why are ...

10

I've heard that gold ore is often associated with quartz veins. What geological processes enable gold particles to naturally cluster together like this? First of all, gold is mostly found in quartz veins in and around igneous intrusions. It happens with a very hot hydro-thermal fluid of silica, oxygen and concentrated gold that is created during ...

10

Double-terminated crystals can from by crystallizing from a melt. The crystallization nucleus has to float freely in the magma chamber. As long as no other crystals obstruct the growth the crystal will grow in its own characteristic form (euhedral). This happens for example with feldspar crystals. (Example: http://www.erdwissen.ch/wp-content/uploads/2010/12/...

9

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 Si, Al, Fe, Mg and Ca. In the figure below I've put them in the MRFE field (Mantle Rock Forming Elements). The trace elements, the elements that occur in very ...

9

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 authoritative review: The process of serpentinization creates strongly reducing conditions and produces fluids that are highly enriched in molecular ...

9

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 oxides are common non-silicate varieties). For a detailed list of mineral species, you should check out the Dana Classification here: Minerals Arranged by the New ...

9

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 these other locations listed below have produced collectible specimens but cryolite does not occur in large enough quantities to be mined. Other important ...

9

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 have markedly violet soils. If you broaden your search to sands as well as soils, there are plenty of examples of garnet-based sands that can appear markedly ...

9

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 things) in sedimentary rocks. This is exactly why you find hydrocarbons... very near the country's shore, on the continental shelf ...because that's exactly ...

9

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 like. but why they stand out from the rest of the stone is beyond me. Because calcite is a translucent mineral, and pectolite is not. You can drop some ...

8

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 solution changes continuously, without any change in crystal habit. Your reference indicates its the size of crystals than matter for being efficient nucleation ...

8

The phosphorous sinks are the ocean and ocean sediments. The ocean holds $3 \times 10^{15}$ moles of phosphorous. The annual amount of phosphorous input into the ocean, as well as the amount of burial of phosphorous as sediment is on the order of $10^{10}$ moles. The sediment is of three categories: Phosphorous associated with calcium carbonate ...

8

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 that are similar to zeolites. The reference also explains that the aluminum phosphate structures grow quickly under hydrothermal conditions of 270-300 degrees C.

8

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 collecting club on Long Island. Someone there would probably know for certain if fluorite can be found. Fluorite can be found in several limestone formations in New ...

8

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) exist on the Moon. This is due to the lack of tectonic activity. Therefore in the Moon you would expect the rocks to be much more homogeneous than on Earth. ...

8

That's amethyst, a violet version of quartz See here

7

This is a big question: it essentially translates to ‘how do we do palaeomagnetism’? I will try to give a brief overview and links to more detailed explanations. I'm also going to focus on the ‘how’, and leave the ‘why’ to someone else (perhaps it would be best split out into a separate question?). To record the geomagnetic field, you need three things: A ...

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