Questions tagged [rocks]

Questions about rock types, formation, chemistry, and physics. If you just want help identifying a rock please use the tag "identification-request".

Filter by
Sorted by
Tagged with
7
votes
3answers
163 views

Is there a widely accepted reason for the formation of tafoni?

Expansion of tafoni seems to be based on weathering (seems reasonable enough.) But what creates them in the first place? There are a number of explanations online (Wikipedia lists eight plausible ...
4
votes
1answer
190 views

Why would CaO be more finely spread than K2O in Granodiorite?

I recently interpreted some XRF data on samples of a granodiorite which were classified under three different types of physical characteristics: very little, mild and significant levels of weathering. ...
1
vote
0answers
56 views

How to identify this rock? [closed]

I am trying to identify this rock. I found it in Alberta. It is basalt? Jade? Or maybe it is extra-terrestrial?
9
votes
1answer
311 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 ...
19
votes
4answers
15k views

What was the first rock in the rock cycle?

I am an undergraduate student but I am a tutor at a High School, and one student asked me. Attempting to explain the rock cycle "if one rock turns into the other then which came first" my gut is ...
6
votes
2answers
77 views

Curious natural patterns on the surface of basalt blocks that make up the sidewalk

During one of my walks through the city streets, I noticed that some basalt blocks that make up the sidewalk have in their surface some very curious natural patterns: The photos above was taken at ...
10
votes
2answers
17k views

How long does it take for a stone to alter?

We see stones and they appear to be the same throughout our life time. Mountains also appear to not significantly change. So do mountains and stones decompose? What is the life span of a stone? After ...
16
votes
2answers
49k views

Are the processes of the rock cycle currently in dynamic equilibrium?

The standard representation of the rock cycle usually looks like this: Does each stage of the rock cycle currently balance? That is, are the various processes in dynamic equilibrium, so that the ...
2
votes
0answers
25 views

What would create the triangles in this rock I found in the Lehigh River [closed]

I collect rocks from the Lehigh Valley River, I have found some many interesting rock. With details that could not be from the water. Can you tell me what would cause the 3 triangle indents on this ...
1
vote
0answers
67 views

How can I find out if this is a geode without breaking it in half? [closed]

I found this rock today on my property. It looks similar to another rock I saw that was said to be a civil war cannon ball, however comments below suggest that it could be a geode. Are there any ...
7
votes
4answers
796 views

How is this crumbly crystal-rich rock formed?

I found this crumbly rock embedded in the channel walls of a small creek in Everett, WA, USA. (North Creek that flows through McCollum Park.) If possible, I'd like to know how the rock formed... what ...
1
vote
1answer
201 views
1
vote
2answers
523 views

How are natural specimens, such as ‘Moqui Marbles’, distinguished from man-made artifacts?

If a particular type of rock specimen is found throughout Earth and is made entirely of natural minerals, but the individual specimens differ minutely from another in size and shape and look to be ...
3
votes
1answer
32 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,...
4
votes
1answer
418 views

Any idea what are these circular rock marks?

During a family trip in the Israeli National Trail in the Pora Stream part (31.496871, 34.770928), I noticed these circular rock marks. Any idea what are they?
3
votes
1answer
187 views

Differentiate a rock and mineral

How to differentiate between a rock and a mineral by merely looking at it as a thumb rule?
4
votes
2answers
887 views

How this sedimentary rock is made?

Apologies in advance for a beginners question. Different rock types make me curious and recently went to an area where interesting sedimentary rock is all over. As the area is on the coast, sea has ...
5
votes
1answer
127 views

Strange coating in old lime mine shaft

Near Prague,Czech Republic is old lime mine. Most of it is closed but one short transport tunnel under one hill is publicly accessible. Tunnel has profile around 2,5x2,5m and it's slightly bended and ...
5
votes
1answer
127 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 ...
5
votes
1answer
106 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 ...
9
votes
3answers
652 views

What do you call boulders of non sedimentary rock that were lithified into sandstone?

I'm convinced there is a word for this. I was in the Hoodoos at Writing on Stone this weekend and kept noticing what looked like reddish quartzite boulders laying around in the sand, or sometimes ...
5
votes
1answer
335 views

What are the circular features in this rock? [closed]

I found this rock by the shore of Lake Ontario. It's light weight and it was grouped with some other rocks with the same patterns.
3
votes
1answer
753 views

What kind of rock is this? [closed]

We found this today in Acton CA USA. Would like to know what it is.
7
votes
3answers
2k views

How was this egg shaped rock made and what is it? [closed]

The following small egg-like rock was found laying on the ground in Tampere, a city in southern Finland. It weights about 950 grams, has a volume of about 360 cm3 and thus a density of about 2600 kg/...
0
votes
1answer
127 views

Identification required, rock formation found whilst on holiday in Cephalonia, Greece white object embedded inside? [closed]

This rock was found in kephalonia Greece, on a beach in lassi. The rock is black in colour, smooth with thumb like prints, very metallic smell and very slightly magnetic. We took this rock to oxford ...
-1
votes
1answer
56 views

Hi please could someone help identify this rock. Received it as a gift from a friend [closed]

The rock has green,purple and white stripes.
1
vote
4answers
542 views

What is this Lake Michigan rock? [closed]

Rock found along northern Lake Michigan, (Charlevoix, MI). Made up of very thin crystalline layers. There are small, round bubble like bumps that protrude from the surface. Doesn't show well in the ...
0
votes
1answer
44 views

If gypsum turns into plaster around 210 F, is there any natural plaster deposits or formations out there?

For a while I have been working with gypsum I mined from a site in Utah, and I realized how low the temperature is to turn it into plaster, so I was wandering; has there ever been any cases of large ...
7
votes
3answers
360 views

Could one say that granites are metamorphic rocks, or not at all?

In my old textbooks, granites used to be part of the metamorphic rocks. Is this still true or not ? If not fully true, to which extent ? Could someone point me towards clear examples or definitions ...
5
votes
4answers
6k views

Why is coal classified as a sedimentary rock?

Something just clicked in my head today. Rocks, by the definition I was taught, are composed of minerals which in turn are by definition not organic, so they are or were not alive. However. Coal, ...
3
votes
5answers
831 views

Where are the oldest igneous rocks found?

I'm trying to catch up on my homework for earth science, but I'm having a difficult time searching for an answer to my question.
3
votes
1answer
692 views

What is the difference between subvolcanic rocks and plutonic rocks?

I'm studying Plutonic (Intrusive) rocks and I really don't understand the difference between Plutonic Rocks that form in Sills and Dikes from the so called subvolcanic rocks, also known as a ...
3
votes
2answers
738 views

What is this white rock with black speckles throughout? [closed]

I was wondering if you have any ideas on what kind of rock this might be? I know that it doesn't effervesce with HCl (no reaction with hydrochloric acid at all) and the size and shape of each grain is ...
0
votes
1answer
112 views

Help me identify my rock is it jade? [closed]

Found this rock it looks like a vein of Jade but I have no idea. This is the inside of the rock. I found it already broke the rock is wet in the pic. It's is a hard rough texture and the green in the ...
0
votes
1answer
453 views

Rock identification: gray with small dark lines/inclusions all over [closed]

Gray stones with short small dark shiny lines all over it. Found it on the beaches of Newport Rhode Island.
1
vote
1answer
33 views

How to calculate or find the compressional stress wave velocity, Cp for a rock

In Cunningham's paper, "The Kuz-Ram fragmentation model - 20 years on", he makes mention of compressional stress wave velocity, Cp. He only comments that the Cp of granite = 5.2 km/s. I using a ...
1
vote
2answers
59 views

Chloride ions for the salty seawater

Where does the chloride ions that are required for the salty taste of sea water come from ? I know that it is the weathering caused by the slightly acidic (due to dissolution of CO2 with water) rain ...
0
votes
3answers
903 views

If rocks are stones, what type of rock are gallstones? [closed]

From Wikipedia: Rock or stone is a natural substance, a solid aggregate of one or more minerals or mineraloids. For example, granite, a common rock, is a combination of the minerals quartz, ...
0
votes
2answers
97 views

Can someone help ID this rock [closed]

Found today in a creek in Indiana, has a geode look and the broken edge shows red opaque facades.
2
votes
0answers
60 views

Is it an egg? What type of rock please? [closed]

This stone was found by my uncle in Western Queensland. It’s light brown in colour and smooth. It's very heavy for its size. 780 grams. Pocket knife doesn’t scratch it. many thanks.
1
vote
0answers
66 views

what type of rock is this? blue/green and brown [closed]

I found this rock while up in the mountains and I have no idea what type of rock it is.
2
votes
1answer
76 views

What is this figurine made of: [closed]

Have several of these animal figurines, MADE IN USSR on bottom. Can't figure out what type of rock it is made from. Any ideas?
6
votes
1answer
800 views

Rock identification: meteorite or lava? [closed]

I was told by a crystal quartz store owner it was a type of lava rock but I have high doubts. hardness: diamond size: 4'' $\times$ 4'' weight: 1.5 lb location: unknown smell: sulfur trait: ...
0
votes
1answer
58 views

Anyone have any idea what these are? [closed]

Can someone please help me identify these rocks please ](https://i.stack.imgur.com/y28zy.jpg)
1
vote
1answer
92 views

Help me to identify this strange rock [closed]

About 9 years ago I found this rock in the middle of the river. It reminds me of a some kind of a volcanic rock, but I live in Finland, and we only have dead volcanoes around here. Outer layer is just ...
1
vote
1answer
27 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 ...
3
votes
1answer
928 views

What's the difference between cleavage and fracture?

I see both terms refereing to fractures on crystals or minerals, so I wonder if they could be considered synonymous. If no, what's the difference between both terms?
1
vote
2answers
117 views

Can anyone identify this stone [closed]

i found this stone on the east coast of south island in New Zealand, it's 200 grams and very hard,i used a metal file on it and it left steel residue on the stone.
0
votes
2answers
72 views

Phase relation for mantle?

I have information about temperature, pressure, normal and shear stresses, viscosity, conductivity, density, heat capacity and adiabatic heating for a particular area of mantle in the form of 2D ...
3
votes
0answers
5k views

What is this black, shiny, smooth, kind of heavy, metallic rock? [closed]

Its kind of heavy for it size, though not extreme - about two pounds. Looks like a chunk of metal, but not quite sure what it is.