Questions tagged [petrology]

Petrology is the study of rocks and the processes that lead to their formation and alteration.

Filter by
Sorted by
Tagged with
1 vote
0 answers
50 views

Estimation of rare earth elements in the SUAC complex

I am currently competing in a case study competition a part of which has asked us to estimate the amount of Nd, Pr, and Dy in the SUAC complex (Sung Valley Ultramafic-Alkaline-Carbonatite) in electric ...
Vijay Arvind's user avatar
4 votes
1 answer
103 views

Why was quartz not a major product of the Lunar Magma Ocean?

Fractional crystallisation generally makes magma more silicic. Why was a substantial quartz layer not a product of the stratification of the Lunar mantle?
Andykins 's user avatar
4 votes
0 answers
33 views

Why are grain coatings an important mechanism for preserving porosity during burial in sandstone but not in carbonate?

I am writing a paper on the role of petroleum emplacement and grain coatings in preserving porosity during burial. I can find many sources discussing grain coatings stopping cementation in sandstone, ...
Coherence1537's user avatar
2 votes
1 answer
99 views

On QAPF (Steckeisen) diagrams, should Albite be considered on the Alkali feldspar or Plagioclase side? Or in-between?

QAPF diagrams are double ternary diagrams used for magmatic rock classification based on mineralogy. Quartz and Feldspathoids are opposed on the pointy ends of the diamond, with Alkali feldspar and ...
Hanatake Yurii's user avatar
5 votes
2 answers
310 views

How is felsic magma produced at island arcs?

I previously believed that continental crust owes its lower density to the partial melting of oceanic crust; the mantle would partially melt at mid-ocean ridges to produce basaltic crust, and when ...
richard's user avatar
  • 51
1 vote
1 answer
103 views

What is the sedimentary form of gabbro/diabase? What would it look like?

Gabbro is an intrusive, mafic, and igneous rock. How would it turn into sedimentary rock?
Lulu M's user avatar
  • 11
4 votes
0 answers
42 views

What is the electrical conductivity of a liquid Komatiite?

I am searching for previous work that has determined the electrical conductivity range for komatiites at the surface. Does anyone have some values or references?
thehungrygraduate's user avatar
3 votes
1 answer
124 views

Are we observing sedimentary rock formation today?

For instance, are we able to see the microscopic accumulation of shale or limestone? Can anyone reference me to sandstone formation observation, that would have to occur more rapidly. I’ve heard it ...
Colin Skinner's user avatar
3 votes
1 answer
498 views

How did this stone become encased within different rock?

My father, in his younger years, was a stone mason in Cincinnati Ohio. A couple of decades ago he was building a wall of some kind. He would fetch rock from a creek bed, haul it to the construction ...
Kenny's user avatar
  • 133
2 votes
1 answer
127 views

Are these igneous Liesegang rings on a popular Oahu, Hawaii hike?

I hiked the Lanikai Pillbox trail (Oahu, HI). I noticed eroded concentric rings in the igneous rock with a hard center. I'm unable to find the geologic cause of these rings. Are they Liesegang rings? ...
user3424230's user avatar
3 votes
2 answers
346 views

regarding four-way closure in structural geology

I am a little bit confused on the two concepts in structural geology, i.e., what is the relationship of anticline and four-way closure. My understanding is that anticline belongs to four-way closure. ...
user297850's user avatar
5 votes
2 answers
147 views

Can we separate a sandy, clayey & salt layer on basis of their rheological properties?

Since, given enough compaction, salt is able to behave like a fluid & buoyant too if it's overlain by a higher density rock (it could be fine grained clay or a sandy sequence). But in another case,...
Diksha's user avatar
  • 101
4 votes
2 answers
195 views

What is the difference between mobile & molten rock?

In the book Fundamentals of Geomorphology (Routledge Fundamentals of Physical Geography) by Richard John Huggett there is a sentence " Intruded rocks, which must be mobile but not necessarily molten,...
Diksha's user avatar
  • 101
3 votes
3 answers
426 views

When sediments are deposited, do they sink into the earth?

I was listening to a geology podcast describing how sedimentary rock forms and later turns into metamorphic rock. As a river lays down sediment, the lower layers can eventually be several kilometers ...
Nathan Long's user avatar
3 votes
0 answers
17 views

Does fold tightness correlate to deformation intensity?

I'm studying a migmatite with two overprinting fold structures. The first (Dn+1) is tight and the second (Dn+2) is gentle. Would it be fair to assume that, since Dn+1's tightness is, well, tighter, ...
Matheus's user avatar
  • 348
1 vote
0 answers
32 views

What are Shoshonites? What conditions make them occur instead of andesites?

What is the significance of shoshonites? Why in some convergent margins, do shoshonites occur instead of andesites?
Muharrem Yavuz's user avatar
1 vote
2 answers
939 views

XRF analysis - recalculating results

For TAS diagram plot, one need to recalculate Major oxide data (NaO, K2O, SiO2). Do one need to recalculate the ppms of Zr,Nb and Y and % of TiO2 for Zr/TiO2 vs Nb/Y diagram plotting for rock ...
Muharrem Yavuz's user avatar
3 votes
2 answers
328 views

Are there any differences between the subalkali and alkali rock occuring tectonic environments?

Here question ends. Beyond details exist Do they occur on the same tectonic regime? For a start to distinguish Subalkali rocks froms Alkali rocks, my knowledge says that mantle is the source of ...
Muharrem Yavuz's user avatar
3 votes
1 answer
55 views

Marks on boulders of volcanic origin

I am working in a catchment in the southern Ecuadorian Andes, about 3700 m.a.sl. Rock outcrops at the upper part of the catchment, as massive blocks varying their size from one meter up to five meters,...
Marlon Calispa's user avatar
4 votes
1 answer
383 views

Why is diabase/dolerite erosion resistant?

Diabase is often considered to be relatively erosion resistant. We can generally find diabase dikes cross-cutting various strata through the geologic landscape, wherein, the diabase dike or sill is ...
MattGeo's user avatar
  • 303
2 votes
2 answers
331 views

How is the difference in crust and mantle composition explained?

We know that the composition of the crust is SiAl and SiMa and the one of mantle is mostly ophiolites, but why? Which are the geological processes that make this difference exist?
Nikolina's user avatar
12 votes
1 answer
561 views

What kind of rock is this being eaten by a rock-eating worm?

The New York Times article This Creature Eats Stone. Sand Comes Out the Other End. describes the shipworm Lithoredo abatanica, an organism that appears to "eat solid rock". It links to the item in ...
uhoh's user avatar
  • 7,096
3 votes
1 answer
141 views

What determines the scale of columnar jointing?

What physical parameters determine the scale of columnar jointing? What makes the columns thinner or thicker? What makes them taller or shorter? What causes the variation in a given site? What ...
jvriesem's user avatar
  • 225
2 votes
1 answer
182 views

could a rhyolitic magma melt a ferromagnesian mineral like olivine?

if the temperature of a felsic magma is about 800-650 °C and olivine melting point oscillates between end members forsterite and fayalite near 1900-1200 °C, Does this mean that an olivine crystal in ...
Coke Lobos's user avatar
2 votes
1 answer
61 views

Why don't pyroxenites and peridotites appear in Streckeisen's QAPF diagram?

Wikipedia says for QAPF diagrams: "A QAPF diagram is a double ternary diagram which is used to classify igneous rocks based on mineralogic composition." Why don't pyroxenites and peridotites ...
user avatar
1 vote
1 answer
56 views

How can I identify "tough" (mixed) granites?

I am trying to parse an old geologic description of stone suitable for use as road metal: Care must be taken to distinguish the difference between the hardness of a stone and its toughness......
Tyler Durden's user avatar
  • 1,804
4 votes
3 answers
294 views

how can a asterisk/star like crack occur on a rock?

how can a asterisk/star like crack occur on a hard pyroclastic rock? Could it caused by a meteroite or by some other mechanism? You may see the shape of the rock on attached photo.
Muharrem Yavuz's user avatar
5 votes
1 answer
433 views

Identification of limestone type

These are images of a stone found and used extensively in the Jammu & Kashmir region between India and Pakistan. These are called devir or devri in the local parlance. Following is the ...
Mohammad Nayef's user avatar
3 votes
2 answers
2k views

Why do we consider hydrostatic pressure and lithostatic pressure separately?

In petroleum geology, why do we consider hydrostatic pressure and lithostatic pressure separately? Surely the pressure at any point, whether fluid or rock, at depth is simply equal the weight of all ...
Gem's user avatar
  • 31
2 votes
1 answer
94 views

Basic petrophysics

The following question was inspired by Effective pressure or what is the effect of presssure?, which may be accessed here: https://inside.mines.edu/UserFiles/File/CRA/2005/...
nate's user avatar
  • 796
2 votes
1 answer
428 views

Difference between thermal and contact aureole

Are therms "contact aureole" and "thermal aureole" synonyms? I found some sentence at A. M. PATWARDHAN (2012): "The peripheral extent up to which the thermal effect of the intrusion is ...
Li Ška's user avatar
  • 21
6 votes
1 answer
4k views

Can cooled/hardened lava rock return to a molten state?

Can lava that has cooled to a hardened state be returned to a molten state by, say, a new river of molten lava flowing over it - like re-smelting iron? If you threw a lava rock into the mouth of a ...
squidlydeux's user avatar
7 votes
3 answers
1k views

In an Earth-like planet with no history of carbon-based life forms, would there be limestone?

The extent of my understanding of limestone is about what Wikipedia says at the very top of the page: Limestone is a sedimentary rock, composed mainly of skeletal fragments of marine organisms such ...
TylerH's user avatar
  • 176
2 votes
1 answer
46 views

What's a reasonable flow rate/mass flux for a fumarole?

Obviously, there is going to be a large amount of variability, but what are some realistic values?
g.z.'s user avatar
  • 380
5 votes
1 answer
96 views

Employment of Volcanologists and Petrologists

What industries or government departments hire volcanologists and igneous petrologists/geochemists in the United States?
Steven's user avatar
  • 53
3 votes
1 answer
591 views

Differentiate a rock and mineral

How to differentiate between a rock and a mineral by merely looking at it as a thumb rule?
gateprep's user avatar
2 votes
3 answers
1k views

What is meant by intraplate volcanism?

I am having massive confusion on whether intraplate volcanism refers to volcanism occurring at plate boundaries or away from plate boundaries (such as formation of ocean island basalts), or perhaps ...
Faraz Gerrard Jamal's user avatar
1 vote
1 answer
554 views

How can I tell the difference between granite and syenite?

(I'm not a geologist, just helping my kids collect rocks).
Lars Nygaard's user avatar
7 votes
1 answer
2k views

Please help in understanding redox buffers

I'm trying to gain a firmer conceptual understanding of how redox buffers work in petrology, specifically how oxygen fugacity influences mineral crystallization. While I understand the mathematical ...
Steven's user avatar
  • 81
3 votes
2 answers
5k views

How do quartz veins form?

Is there an association with thrust fault or dormant volcanos and quartz veins? Where are quartz veins likely to occur in nature and how are the formed? Is it possible to identify these veins from ...
Jeffrey Boettger's user avatar
2 votes
1 answer
60 views

Effect of reducing conditions on melting point

I've been reading a paper(*) looking at the deep carbon cycle and it mentions a key process that the authors refer to as "redox melting". According to the paper, reducing conditions increase the ...
Graham's user avatar
  • 66
16 votes
0 answers
3k views

What is the global distribution of oil filled geodes?

In a general 40 mile radius of Keokuk, Iowa many sedimentary geodes can be found. They are abundant in the Warsaw Formation with the type section at Geode Glenn in Warsaw, Illinois. In one specific ...
user avatar
6 votes
1 answer
4k views

How did the terms "acidic" and "basic" come to be associated with $SiO_2$ in igneous rocks?

Students of geology are introduced to in their petrology course, (or used to be), to the terms "acidic", "basic", and the associated term "intermediate" in relation to %$SiО­­­_{2}$ in igneous rocks, ...
My Other Head's user avatar
6 votes
1 answer
141 views

There are cloud identification guides, are there also (guided) rock identification websites?

Seeing all these rock identification questions, got me wondering, is there no straightforward guided rock identification website? In Intro to Geology lab, I remember going through a bit of a process ...
JeopardyTempest's user avatar
1 vote
2 answers
82 views

Where can I get mineral testing done? [closed]

Where can I send a sample of material to be tested to see exactly what it is? Do you have an address where items can be sent for testing and evaluation? I have a softball size rock that was given to ...
James Fields's user avatar
1 vote
1 answer
1k views

Crystallization path of diopside-wollastonite-silica systems

Can someone please explain to me (or give a source) how the crystallization diagram of the diopside-wollastonite-silica system looks. I am a new learner of geology and trying to learn ternary systems.
Pranav Shekhar's user avatar
5 votes
0 answers
103 views

What causes a change in composition from basanite to nephelinite?

Can the change in composition from basanite to nephelinite (i.e. increasing alkalis with decreasing SiO2) be explained in terms of fractional crystallisation, or only by a decreasing degree of partial ...
Leticia's user avatar
  • 51
4 votes
1 answer
2k views

What are the differences in terms of appearance between sandstone and limestone?

On the field, I find it very difficult to differentiate the two types of rocks just by looking at them.I know that you should do some analysis of the sample before any conclusions. But, for example in ...
Andres Romero's user avatar
4 votes
1 answer
86 views

Is a controlled fractional crystallization process feasible on the Moon?

I am looking for a way to separate metal oxides on the Moon. Please bear with me - it's for an ultra-hard science fiction project. Processes typical on Earth are not effective there. Heat is cheap on ...
kim holder's user avatar
4 votes
1 answer
2k views

Does ground-to-cloud lightning create crystals as well?

I've read that cloud-to-ground lightning can create fulgurites. Does ground-to-cloud lightning also create crystals within the earth as it surges through the minerals?
Melissa Koski's user avatar