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In the first paragraph, should graphene be considered a different allotrope of graphite? Or simply a smaller crystal of graphite constrained from vertical growth. —Preceding unsigned comment added by (talk) 05:51, 4 May 2011 (UTC)

Clearly, steam, water, and ice are not allotropes. However, what about the various solid phases of water (ice(I), ice(II), etc...)? I believe they would be considered polymorphs, but probably not allotropes because water isn't a pure element. Is this correct? --Matt Stoker

Right. Allotropy refers specifically to elements. I double-checked my understanding of this with the Penguin Dictionary of Chemistry (DWA Sharp, Penguin:1990 ISBN 0-145-051232-2), but I'd encourage anyone to consult whatever credible reference they feel necessary. --JoeAnderson

The last edit of this page commented "allotropy and isomerism are *distinct*" -- yes, but how? Roughly, is it the case that two allotropes will have completely different chemical properties (diamond vs carbon), while isomers tend to have similar properties (similar boiling points, etc)? -- Tarquin, Sunday, July 7, 2002

It is suggested that we consult the MACMILLAN ENCYCLOPEDIA of CHEMISTRY edited by J.J.Lagowski, 1997, SIMON SCHUSTER for a definitive exposition of the subjects ALLOTROPES and POLYMORPHS. It is pointed out that there is no phenomenon that results in the existence of ALLOTROPES. Allotropes exist as a result of the differing chemical bonding of the same atoms. --Anon

Why is "allotropy" a misnomer? -phma

The first paragraph of this article needs to be clarified. 13:42, 17 January 2006 (UTC)

This article indicates that allotrops can exist in the the solid, liquid, or gas phases. Is this true? I have been led to believe that allotropy specifically relates the structure of the solid matrix. for example for Fe: alpha-ferrite (BCC) gamma-austenite (FCC) delta-ferrite (BCC) are all allotropes > However, I have not been able to find information confirming nor contradicting this. The text I am using as a reference is Structures and Properties of Engineering Alloys Second Edition by Smith ISBN 0-07-059172-5

Yes, those phases would be allotropes, but only when talking about pure iron. In metallurgy, it's generally preferred to use the term "phase" as opposed to "allotrope" to avoid ambiguity. Allotropes are distinct chemical species with varying reactivities and physical properties. Allotropes can be present in any phase, but some become unstable in certain phases and will transition into a more energetically favourable structure. Hope this helps. --Xanthine 00:10, 1 May 2006 (UTC)

I have a doubt whether the amorphous state of some element (let's say C) can be called an allotrope of that element; shouldn't "allotrope" be used just for different crystalline forms? comparing amorphous and crystalline ... isn't it a bit like comparing liquid and solid? for polymorphism this doubt does not exist and indeed the term refers only to different crystalline forms of the same compound.

16:38, 16 April 2013 (UTC)G — Preceding unsigned comment added by (talk)

The question is not what makes sense to Wikipedia editors, but rather how does the scientific literature use the term. The article now implies that the term is NOT restricted to crystalline phases, and is even used for gases such as dioxygen and ozone (trioxygen). If this is incorrect, we need reliable sources which say so explicitly. Dirac66 (talk) 22:11, 16 April 2013 (UTC)

Allotropy - isomers[edit]

The term allotropy is usually only used for elements. In the case of compouds, the analogous term would be isomers. Andreas 02:25, 26 January 2006 (UTC)


What exactly needs expert attention? kotepho 01:57, 25 March 2006 (UTC)

Erm... For a start, until recently the definition said a lot more about what allotropy isn't than what it actually is... --Xanthine 23:11, 30 April 2006 (UTC)

Major Cleanup[edit]

I believe I'm suitably qualified to be an expert on this subject. I have done a large scale cleanup of this article, tidying up any discrepancies and clarifying a number of points. I think it reads a lot better now. If you notice any errors (factual or grammatical), please do let me know. And feel free to correct them. --Xanthine 00:10, 1 May 2006 (UTC)

Usually ...[edit]

The article illustrates allotropy with two crystalline forms of Fe, but my impression is that usually allotropy refers to molecules or low dimensional materials. It can be assumed that all elements exhibit polymorphy, especially at high pressures. So while formally allotropy (isomerism for elements) is widespread, for instructional purposes, the discussion is usually limited to species existing as molecules (S, Se, As, P, C, O).--Smokefoot (talk) 13:09, 20 December 2007 (UTC)

Molecules or covalent solids (diamond is not a molecular solid, unless you call the entire crystal a very big molecule!) But I've never seen the term applied to metals. --Itub (talk) 16:37, 20 December 2007 (UTC)
I just found that many books do speak of allotropes of iron.[1] These are often books on metallurgy and related topics. It is true, however, that most general chemistry textbooks only seem to give examples of allotropy among nonmetals. --Itub (talk) 09:58, 9 January 2008 (UTC)

References for metals[edit]

Are there any references for the metal allotropes? Even in the crystallography open database and the inorganic crystal structure database there is no structure for strontium other than the cubic. (talk) 15:19, 19 August 2008 (UTC)Jared Hansen

Definition of Allotropy??????[edit]

It is saying that in the definition the word "chemical elements", but silica (SiO2) is not a element. But it has allotropic forms??????????? —Preceding unsigned comment added by Shivaaprs (talkcontribs) 03:24, 10 July 2010 (UTC)

The article refers to the element silicon (Si), not the compound silica which is the short name for silicon dioxide (SiO2). Dirac66 (talk) 12:27, 10 July 2010 (UTC)

Allotropy vs polymorphism[edit]

User today added a [who?] to ask who are the many other chemists who have repeated Ostwald's advice to replace the term "allotropy" by "polymorphism". The sentence which is questioned was added by me on 18 May 2007. It is a paraphrase of Jensen's 2006 article, which refers to "sage advice, which many have since repeated", with a reference to a 1964 book "The allotropy of the elements" by W.E. Addison. I will add a reference to indicate the source of this sentence and the word "many", even if Wikipedia does not identify the many. Dirac66 (talk) 00:31, 1 February 2012 (UTC)

What does this mean ?[edit]

"Allotropes are typically more noticeable in non-metals ..." Does it mean that we are more likely to notice the difference in the cases of non-metallic allotropes, or that non-metals are more likely to exhibit allotropy ? (talk) —Preceding undated comment added 06:27, 16 September 2013 (UTC)

A revision history search shows that this phrase was added on 30 April 2006 by Xanthine who has been inactive on Wikipedia since 2009. So we are unlikely to have a reply from the author of this phrase. I think that this and the following sentence about metals should just be deleted, unless someone can provide a clearer statement about the occurrence of allotropy in non-metals and in metals, preferably with a source. Dirac66 (talk) 10:58, 16 September 2013 (UTC)
Done. Dirac66 (talk) 00:25, 31 January 2014 (UTC)

Sigma tin[edit]

What is sigma tin? I don't seem to be able to find anything about it. Except from Sigma Tin Alloy Manufacturers (Pte) Ltd which is located in Singapore. Grey tin AKA tin pest is stable below 13C to -274. White tin (normal tin) is stable between 13C and 161C and Rhombic tin is stable between 161C and melting point. This doesn't leave much space for sigma tin. — Preceding unsigned comment added by (talk) 08:00, 29 January 2014 (UTC)

First, I have moved this comment down to a new section at the end of the talk page. The data you cite for grey, white and rhombic tin is for pressure = 1 atm. However the article on Tin mentions a σ phase at very high pressures. I checked the (translated Russian) source and the σ phase is stable at over 40 GPa (= 4 x 105 atm). I will add a note to this article with the source.
And I doubt that the company in Singapore works at such high pressure. Probably the use of Sigma is a coincidence and they just chose the name arbitrarily, or perhaps because Sigma sounds like Singapore Dirac66 (talk) 00:25, 31 January 2014 (UTC)