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Geology in general

Posted by Anonymous User  
Anonymous User May 10, 2012 08:37PM
Is it ok to ask opinions about geology in general ? if not can anyone tell me of any decent geological discussion forums.

Edited 1 time(s). Last edit at 05/10/2012 08:43PM by Heath Barnes.
Ralph Bottrill May 11, 2012 01:39AM
Fire away! We have a few geologists on board.

Kelly Nash May 11, 2012 02:29AM
That would be a breath of fresh air after all the questions about treasure hunting, crystal healing, and evil bureaucrats we usually see here.

- Kelly Nash (Geologist)
Tom Goodland May 11, 2012 06:14AM
This is a request to any geologist/petrologist out there.

I mostly like collecting minerals but often come across attractive and intriguing rocks. Does anyone know of a website which describes, with good colour photos, all the myriad different types of rocks found around the world. Info on each, such as constituent minerals, type of geological formation & distribution would be very useful. A search for such websites came up with sites with only a few common rocks aimed at children.

I also like collecting fossils (i have very catholic tastes!). Is there anything similar to Mindat but for fossils (Fosdat)? I know palaeontology is a vast subject with probably even more contentious issues around collecting (exactly where a fossil comes from being all-important for scientific value).


tom goodland
Becky Coulson May 11, 2012 10:07AM
Hi Tom,
Like you, I enjoy collecting rock samples in addition to minerals - and they are often more difficult to identify because of their varying composition! I have yet to find a decent website along the lines of Mindat, with specimen photos from specific localities uploaded. Although some universities, museums, etc. have uploaded their own collections and slides, I don't know of a petrology website - I hope someone can help us with this! I have a real interest in volcanics, and have had to rely heavily on field guides and local experts to help me. I keep dreaming of finding a book along the lines of "Volcanoes and their products", with samples from individual sites. Becky
D Mike Reinke May 11, 2012 11:59AM
I think the 'problem' with rocks is that everything grades into everything else, or at least seems to to me, and defining boundaries is difficult.
I know of no site like you've looked for, only very scattered info in books. Simon & Schuster's guide to rocks is well illustrated, I think.
A general site you might like is Raymond Wiggers' site. He gives outstanding slide shows, just caught one at the local library, and his book, and picture captions are a good read. Not an analysis of rock types, but an appreciation of them.
Norman King May 11, 2012 12:40PM
It is also true in paleontology that everything grades into everything else. Shades of difference between species are matters of opinion, and only the opinions of those specializing in certain groups are worth listening to (I'm not being facetious!).

After working with the Cretaceous pelecypod family Inceramidae, it took about ten years before anyone came to me for ID's. Even then, if I said that Mytiloides lusatiae (for example) occurs in the basal Fort Hays Limestone in Colorado and New Mexico, many people would ask me by whose authority I could say that. Turns out it doesn't occur there, but American workers, including myself, thought so until recently Ireneusz Walaszczyk of Poland, working with Bill Cobban of the US Geological Survey, determined that species had been Mytiloides scupini all along.

Such is the ridiculous "game" that goes on in paleontology, and that is the reason, when I had the option way back in the 1970's of specializing in either paleontology or physcial stratigraphy (including many aspects of sedimentology), I chose the latter. Nevertheless, it is probably still true (as it was in the 60's, 70's, and 80's) that stratigraphic paleontologists make more money in the petroleum industry that almost any other specialty. That is because so few people could do it. But I could! (And, paradoxically, it would never had made any difference what we called that stupid species of Mytiloides).
Ralph Bottrill May 11, 2012 01:37PM
Many minerals grade into one another too, there is not much in the world that is completely black and white!

The problem with rocks is that to categorise them properly you really need a thin section, polarizing microscope and often a full chemical analysis, else you are just guessing. Guessing based on macroscopic appearance may be good enough if you are happy to call something a broad name like basalt, granite or sandstone, but you still need a good hand lens and a few physical tests. Most basic geology and mineralogy books & websites give the basics of rock classifications, some illustrated, but a macrophoto of a basalt may not look much different to some sandstones, mudstones, quartzites, limestones, hornfels etc.

There is a place still for a Rockdat type database still, IMO, with photos and thin sections of rocks from various places; I dont know of anything existing that approaches this.The trouble is we need to get a few more geologist on board, most of us have too much to do with mindat still!

Kelly Nash May 11, 2012 01:58PM
For fossils, I do wish there was a "FossilDat". It would be a huge job, but probably not a whole lot more than Mindat in the long haul, as long as you accept that one can classify most fossils. The last time I looked, you have Kingdoms, then Phylum, Class, Order, Family, Genus, and Species. There are useful distinctions even at the Class level, for example pelecypods vs. brachiopods. As Ralph points out, with rocks, particularly fine-grained rocks, you will often need to be familiar with the local geology to even know for sure if you're looking at an igneous, sedimentary or metamorphic rock in a hand specimen. But a "RockDat" would be handy too, as long as it included some thin sections, and also assuming the people-power available to build it.

For both fossils and rocks, if you're trying to identify things in a particular area, you may be better off finding a good field guide to the geology of the area (or a human guide) rather than a rock or fossil book. That also helps a lot with minerals, but at least with minerals, once you have seen enough of them, you begin to recognize a good number of them (especially if they are crystals) no matter where you are, though you may sometimes have to supplement your visual ID with testing.
Alex Homenuke May 11, 2012 02:42PM
Rocks are absolutely fascinating. They are made up of minerals (see Mindat for more info). One must understand the processes that form rocks to be able to properly classify them. Rocks also record the history of the earth and for many billions of years the history of the universe (what happened before that only "god" and one or two physicists know). Some rocks incorporate plants and animals into their structure. These rocks are called fossils. (see Norman King above). Metals can be removed from rocks and used to improve our lives. This is called mining and smelting. Sometimes plants and micro-organisms exude hydrocarbons when they are incorporated into rocks. This becomes gas and oil, which also makes our life better. People who pretend to understand all these processes and their results are called geologists. Some people just collect minerals and rocks because they are pretty. Others call them nuts, so they join Mindat where they can converse with people who understand them.

I have no idea what came over me to write this (Al, a geologist)
Paul Brandes May 11, 2012 07:53PM
I'm not sure either Alex, but I couldn't have said it better myself!! :)-D
Heath; please ask your geology questions here. As Kelly mentioned it will be a very refreshing change of pace.

Edited 1 time(s). Last edit at 05/11/2012 07:55PM by Paul Brandes.
Anonymous User May 11, 2012 08:44PM
I have been studying the geology of the south east area of Cleveland north east England for the last year and a half using the deep beck valleys, what i have found is controdictory in every way to the British geological survey mapping of the area, the accepted landscape is mapped as being till covered with icolated lacustrene and aluvial deposits. I have found this not to be the case the area is in fact covered with a sucsession of almost stoneless seperate aluvial deposits that sit above a gravel bed that avarages 300-400 mm thick this gravel bed is rich in fossils mineralized bone and preserved organic material, beneath the gravel bed is a red clay.
Also the gravel bed contains a lot of magnetic material mostly basaltic andesite, that i believe origionated from the nearby Cleveland dyke the dyke formed 58 mya and ive found the stone attracts a weak magnet quite easilly, ive tested 4 different outcrops but the dyke at my home area is by far the most magnetic.
Norman King May 11, 2012 10:17PM

Do you have any photos of the gravel bed and the alluvial material above it? That would sure help me in understanding what you have found.
Martin Rich May 11, 2012 10:42PM
try this (english is available):

Anonymous User May 11, 2012 11:17PM
Yes i have a blog full at i will now be posting images but the blog is there to trawl through if anyone whants to. and thanks for the interest
Anonymous User May 11, 2012 11:19PM
Martin Rich Wrote:
> Heath,
> try this (english is available):
> he.html
> Martin thanks i will try them.
Tom Goodland May 12, 2012 06:07AM

thanks for the link (a database of 4500 rocks from round the world). I'm not sure of its usefulness when trying to identify rocks but it's interesting, as my "day job" is a builder!

Ralph Bottrill May 12, 2012 10:09AM
Don't forget if you search Google images you will get photos of most rock types, and many thin sections too. You have to sift through a lot of junk though.

Erik Vercammen May 12, 2012 10:38AM
See : in Dutch, but also English
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