Understanding through Discussion

Welcome! You are not logged in. [ Login ]
EvC Forum active members: 90 (8839 total)
Current session began: 
Page Loaded: 05-27-2018 9:46 AM
235 online now:
dwise1, edge, JonF, kjsimons, Modulous (AdminModulous), Percy (Admin), xongsmith (7 members, 228 visitors)
Chatting now:  Chat room empty
Newest Member: Calvin
Post Volume:
Total: 832,570 Year: 7,393/29,783 Month: 1,617/1,708 Week: 20/488 Day: 20/77 Hour: 2/1

Thread  Details

Email This Thread
Newer Topic | Older Topic
Author Topic:   Introduction To Geology
Member (Idle past 140 days)
Posts: 888
From: Birmingham, England
Joined: 09-21-2011

Message 286 of 293 (720184)
02-20-2014 5:22 PM
Reply to: Message 283 by Dr Adequate
02-20-2014 1:04 PM

Re: Wikibook
#9 on Google.co.uk

Could there be any greater conceit, than for someone to believe that the universe has to be simple enough for them to be able to understand it ?

This message is a reply to:
 Message 283 by Dr Adequate, posted 02-20-2014 1:04 PM Dr Adequate has not yet responded

Posts: 1766
From: Ontario Canada
Joined: 08-04-2010

Message 287 of 293 (720191)
02-20-2014 6:24 PM
Reply to: Message 283 by Dr Adequate
02-20-2014 1:04 PM

Re: Wikibook
#8 on Google.ca
This message is a reply to:
 Message 283 by Dr Adequate, posted 02-20-2014 1:04 PM Dr Adequate has not yet responded

Posts: 19487
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 2.5

Message 288 of 293 (720195)
02-20-2014 7:10 PM
Reply to: Message 283 by Dr Adequate
02-20-2014 1:04 PM

Re: Wikibook
nothing on page 1 for historical geology from BING

but #1 for historical geology wikibook

Edited by RAZD, : bing

we are limited in our ability to understand
by our ability to understand
Rebel American Zen Deist
... to learn ... to think ... to live ... to laugh ...
to share.

Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click)

This message is a reply to:
 Message 283 by Dr Adequate, posted 02-20-2014 1:04 PM Dr Adequate has not yet responded

Posts: 5676
From: UK
Joined: 10-07-2011
Member Rating: 2.3

Message 289 of 293 (720220)
02-21-2014 2:54 AM
Reply to: Message 283 by Dr Adequate
02-20-2014 1:04 PM

Re: Wikibook
#9 from the UK although I wouldn't know to use that term to search myself.

If I was searching for a starter on geology I'd probably use your thread title - 'introduction to geology' - but those key words are very competitive.

Good job tho'....very good.

Life, don't talk to me about life - Marvin the Paranoid Android
"Science adjusts it's views based on what's observed.

Faith is the denial of observation so that Belief can be preserved."
- Tim Minchin, in his beat poem, Storm.

This message is a reply to:
 Message 283 by Dr Adequate, posted 02-20-2014 1:04 PM Dr Adequate has not yet responded

Posts: 222
Joined: 11-13-2011
Member Rating: 3.3

Message 290 of 293 (745584)
12-24-2014 3:00 PM
Reply to: Message 282 by Pollux
01-05-2014 6:47 PM

Hi Dr A.
I am currently going through your excellent book.
In the article on Reefs, it says rudist bivalves went extinct at the Cretaceous -Triassic boundary. Should it not be C-Tertiary?
This message is a reply to:
 Message 282 by Pollux, posted 01-05-2014 6:47 PM Pollux has acknowledged this reply

Replies to this message:
 Message 292 by Dr Adequate, posted 12-24-2014 3:33 PM Pollux has acknowledged this reply

Inactive Member

Message 291 of 293 (745586)
12-24-2014 3:10 PM
Reply to: Message 283 by Dr Adequate
02-20-2014 1:04 PM

Re: Wikibook
#4. First is the general Wikipedia page on Historical Geology; 2 and 5 are links to random university courses; and 3 is a link to Amazon.

So not only amongst the top five, but one of only two I think most people would even consider clicking on. Nice.

Love your enemies!

This message is a reply to:
 Message 283 by Dr Adequate, posted 02-20-2014 1:04 PM Dr Adequate has not yet responded

Dr Adequate
Posts: 16015
Joined: 07-20-2006
Member Rating: 3.3

Message 292 of 293 (745591)
12-24-2014 3:33 PM
Reply to: Message 290 by Pollux
12-24-2014 3:00 PM

Re: Wikibook
In the article on Reefs, it says rudist bivalves went extinct at the Cretaceous -Triassic boundary. Should it not be C-Tertiary?

It surely should. Thanks.

In my defense, they both begin with T.

This message is a reply to:
 Message 290 by Pollux, posted 12-24-2014 3:00 PM Pollux has acknowledged this reply

Posts: 10772
From: Denver,Colorado USA
Joined: 12-30-2003
Member Rating: 1.2

Message 293 of 293 (823992)
11-20-2017 10:57 PM
Reply to: Message 44 by Dr Adequate
10-14-2011 2:09 AM

REMIX: Introduction To Geology
Dr, Adequate started this informative topic, and I wanted to summarize it here:
Dr.Adequate writes:

I should like to give an introductory course on geology.
It will consist of a series of articles presented in what I think is the right order for teaching geology. I shall present them perhaps at weekly intervals, except for the first few which will merely clarify definitions and which we can get through quickly. (...)

Course objectives

The objective of this course is to show how it is possible to reconstruct the past history of the Earth from our present observation of the rocks.

It will differ from other textbooks in that it will place a strong emphasis on asking and answering the question: "How do we know?" Most textbooks report certain aspects of geological knowledge simply as things that are known: for example, that granite is an igneous rock, or that sandstone with certain properties is aeolian; or that the Earth's core is iron; but without addressing, or at least without systematically addressing, the question of how these things are known in such a way as to satisfy the doubts of the skeptical or the inquisitiveness of the curious.

As a result, the average geology textbook does fairly poor service to the skeptical, or to those who wish to debate and convince the skeptical. It also, in my view, does a disservice to the science of geology itself: for the story of geology is in effect the world's longest-running detective story, and it is more interesting if geology is presented as such than as a collection of facts handed down from on high.

Course outline

Finding the right order in which to structure a course in geology is perhaps the most perplexing decision facing its author. No solution is ideal, because (with the exception of the definition of basic terms, which clearly should come first) it would be best if every topic could be discussed last, so that the reader can come to it with the rest of the course as context. As this is impossible, some sort of compromise has to be made.

The contents of the course will be as follows:

(1) Rocks and minerals: in which I explain what is a mineral, what is a rock, what are sedimentary, igneous, and metamorphic rocks.

(2) Surface processes: including weathering and erosion, rivers, glaciers, nearshore processes, marine sediments, etc; with a systematic look at all the different types of sediment and their corresponding sedimentary rocks --- peat and coal; glacial till and tillite; deserts and aeolian sandstone; coccoliths and chalk; etc, etc, etc.

(3) Plate tectonics: in which we describe how it is known that plates move, what is know of the mechanisms, and what effects this has in terms of faulting, folding, orogeny, ophiolites, terranes, etc.

(4) Stratigraphy: a discussion of actualism, of Steno's principles, of way-up marks, of cross-cutting relationships, of the geological column, of index fossils, and so forth.

(5) Absolute dating: those dating methods other than the relative methods of stratigraphy. This will include a look at some of the methods of more doubtful value, such as racemization.

(6) [This is added by edit in November] I shall have to add a section, hopefully a short one, about paleoclimatology. This is something of an afterthought, but having written much of the rest of the course and repeatedly said that such-and-such a thing would be put off until I talk about paleoclimatology, I don't see how I can not talk about it. So be it.

At that point I shall have done what I set out to do, in that the reader will then have a grasp of the principles of historical geology. However, it may be that the readership will have further questions. In particular, the reader may want to see some historical geology actually done, or in other words to see some case studies. It may be possible to continue the discussion along these lines.

Note on sources

It will not be necessary to give references for notions which are the common property of geologists, such as the definition of a mineral or the fact that granite is felsic. However, I shall provide references to the more abstruse or particular facts to which I allude.


Thanks are due to Pressie for volunteering to review the material. Any remaining errors are, of course, mine. As a great man once said: "We all have our little faults".


Minerals and rocks: definitions

Pressie writes:

I think we should provide the "official" geological explanations of the words crystal and mineral.

Crystal: A homogenous, solid body of chemical element, compound, or isomorphous mixture, having a regularly repeating atomic arrangement that may be outwardly expressed by plane phases.

Isomorphous mixture: Two or more crystalline substances to have similar chemical composition, axial ratios, and crystal forms, and to crystallize in the same crystal class. Such substances form an isomorphous series.

Mineral: (a) a naturally occurring inorganic element or compound having an orderly internal structure and characteristic chemical composition, crystal form, and physical properties. Those who include the requirement of crystalline form in the definition would consider an amorphous compound such as opal to be a mineraloid.
(b) Any naturally formed inorganic material, i.e. member of the mineral kingdom as opposed to the plant and animal kingdoms.
From Bates, R.L. and Jackson, J.A. (Editors), 1980. Glossary of Geology, Second Edition. American Geological Institute. Falls Church, Virginia.

This makes organic material such as amber a mineraloid, not a mineral. Any organic material, such as coal, therefore is not a mineral (although used as such colloquially).

Silicate minerals
Silicate structures

By a silicate tetrahedron we shall mean an atom of silicon bonded with four equally spaced atoms of oxygen forming the four corners of a pyramid having a triangular base.

Each tetrahedron can share each one of its oxygen atoms with one other tetrahedron, so that two tetrahedra can join together corner-to-corner (but not edge-to-edge or face to face). Hence each tetrahedron can be linked with up to four other tetrahedra, one for each corner of the tetrahedron; or three, two, one, or none. This gives us a wide variety of structures that can be built out of tetrahedra: three-dimensional lattices; two dimensional sheets, chains, double chains, rings, et cetera; so silicate minerals can be classified according to their silicate structure as lattice silicates, sheet silicates, chain silicates, and so forth. The diagram below shows some of the possible structures.

Key: (a) an isolated tetrahedron; (b) a pair; (c) a six-member ring; (d) a chain; (e) a double chain; (f) a sheet.

Note that the chain and double chain can be extended indefinitely in one direction and the sheet in two directions.

A silicate mineral is a mineral containing silicate structures. Note that with the exception of quartz and its polymorphs, a silicate mineral will not consist entirely of such structures. Atoms of other elements must necessarily be involved so that the rings, chains, sheets or whatever form part of a three-dimensional crystal.

Most silicate structures can be described either by a descriptive English name such as "sheet silicate" or by a name which describes the same thing in Greek such as "phyllosilicate". Where a plain English term exists, I shall employ it in this text. The table below shows how the structures relate to the English and Greek names and gives examples of minerals important to this course.

Structure English name Greek Important examples
Three-dimensional Lattice silicates Tectosilicates Quartz; feldspars
Parallel sheets Sheet silicates Phyllosilicates Micas; clays; serpentine; chlorite
Single or double chains Chain silicates Inosilicates Pyroxenes; amphiboles
Three, four, or six-membered rings Ring silicates Cyclosilicates
Pairs Sorosilicates Epidotes
Isolated tetrahedra Nesosilicates or orthosilicates Olivine

Because tetrahedra link together by sharing the oxygen atoms at their corners, the structure formed by the tetrahedra is reflected in the chemical formula of a silicate. For example, quartz consists of nothing but tetrahedra linked together in a three-dimensional lattice. This means that every tetrahedron is linked to another at all four corners; which means that every oxygen atom is shared by two silicon atoms; which means that quartz has the formula SiO2. Similarly, if you look at the formula for zircon (ZrSiO4) you can see that it must be a neosilicate.


In some silicates, the structure is based not just on silicate tetrahedra but also on tetrahedra with a central atom of aluminum rather than silicon. Silicates which incorporate these aluminum-based tetrahedra as well as silicate tetrahedra are known as alumnosilicates.

Aluminum-based tetrahedra have a different charge from silicate tetrahedra. This means that you cannot have an aluminosilicate which differs from an ordinary silicate only by the substiution of atoms of aluminum for some of the atoms of silicon; there must necessarily be other differences. For example, it is chemically impossible to build a lattice just out of these two kinds of tetrahedra analogous to quartz; other atoms are required to balance the charge of the chemical formula. Hence lattice aluminosilicates such as feldspars do not have the formula (Si,Al)O2, which is impossible, but have formulas such as KAlSi3O8 and CaAl2Si2O8.

Felsic and mafic silicates

Silicate minerals which are high in silicon are called felsic minerals; the opposite of felsic is mafic; minerals which are very mafic are known, sensibly enough, as ultramafic. Note that this term only applies to minerals which are silicate minerals and so contain some silicate tetrahedra; no-one would call calcium carbonate (for example) an ultramafic mineral.

In some texts, particularly older texts and British texts, you may see the words acidic, basic, and ultrabasic used instead of felsic, mafic, and ultramafic. These terms refer to an obsolete hypothesis of mineral formation, and I shall not use them; I mention them only for the benefit of those readers who might come across them in further reading.

Some generalizations might be made about the differences between felsic and mafic minerals: as we progress from felsic to mafic the minerals are more dense (because the atoms in them which aren't oxygen or silicon are heavier elements such as magnesium or iron); they have higher melting points; and when they do melt they are less viscous (that is, they flow more easily).
Rocks: igneous, sedimentary and metamorphic

In this article we shall look at the most significant way in which geologists classify rocks. The reader should recall from the article on minerals and rocks that a rock is an aggregate of one or more minerals or mineraloids.

Igneous, sedimentary, and metamorphic

There are all sorts of ways that we might classify rocks. We might, for example, divide them up according to chemistry: and indeed the distinction between silicates and carbonates is a useful one. We might also classify rocks according to whether they contain felsic or mafic minerals, and as we shall see this is a good way to classify certain rocks. But the most fundamental way in which geologists classify rocks is to label them as igneous, sedimentary, or metamorphic.

Igneous rocks are rocks formed by the cooling and setting of molten rock.

Sedimentary rocks are formed by sediment (for example, sand or mud) turning into rock (such as sandstone or mudrock).

Metamorphic rocks are formed when rocks are subjected to heat, to pressure, to chemical reactions, or to any combination of these three, in such a way as to change the properties of the original rock in some way.

The rock cycle

The relation between the various kind of rocks can be summarized by a diagram of the rock cycle. Here is one picture of it which I find more or less satisfactory; I may at some point come back to this and prepare my own.

How do we know?

At this point we are touching on the main theme of this course. For to classify rocks as igneous, sedimentary, or metamorphic is implicitly to classify them not by their directly observable properties such as color or density or chemical composition --- but by their history as inferred from their present-day properties. The reader will, therefore, want to know: how do we know? This question will be answered in separate articles on igneous, sedimentary, and metamorphic rocks.

In the meantime, let us point out how intrinsically historical geology is. After we've got past the most basic of considerations such as defining a mineral and defining a rock, we are plunged into historical considerations. And this in not just because this course is about historical geology: it would be the same if it was an introduction to how to find oil. There is no geology that is not historical, and if we tried to do without historical inferences we might as well classify rocks by how pretty they are for all the good it would do us.


Chance as a real force is a myth. It has no basis in reality and no place in scientific inquiry. For science and philosophy to continue to advance in knowledge, chance must be demythologized once and for all. RC Sproul
"A lie can travel half way around the world while the truth is putting on its shoes." Mark Twain "
~"If that's not sufficient for you go soak your head."~Faith
Paul was probably SO soaked in prayer nobody else has ever equaled him.~Faith :)

This message is a reply to:
 Message 44 by Dr Adequate, posted 10-14-2011 2:09 AM Dr Adequate has not yet responded

Newer Topic | Older Topic
Jump to:

Copyright 2001-2015 by EvC Forum, All Rights Reserved

™ Version 4.0 Beta
Innovative software from Qwixotic © 2018