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Basalt is an extrusive igneous rock, sometimes porphyritic, and is often both fine-grained and dense. Basalt in the tops of subaerial lava flows and cinders will often be highly vesiculated, imparting a lightweight "frothy" texture to the rock. The term basalt is often casually applied to shallow intrusive rocks with a composition typical of basalt, but rocks of this composition with a phaneritic groundmass should generally be referred to as gabbro. The crustal portions of oceanic tectonic plates are predominantly made of basalt. Frankly, I do not get a word of what it means. Thankfully I know what Basalt is.— Preceding unsigned comment added by (talk) 07:06, 30 September 2005

There you go. Hopefully even oompa loompas can read it and know what it is now.Rolinator 09:12, 22 January 2006 (UTC)

Basalt (IPA: /ˈbæsɒlt, bəˈsɒlt/) is a common gray to black extrusive volcanic rock. It is usually fine-grained due to rapid cooling of lava on the Earth's surface. Basalt isn't extrusive. The word "Basalt" is based on the chemial composition and grainsize, not if it was formed on the surface or underground. It isn't usually fine-grained, by defintion it is fine-grained. If it was medium/coarse grained it would be a dolerite/gabbro.— Preceding unsigned comment added by (talk) 04:47, 3 July 2007

Transitional alkalic basalts[edit]

Image:Volcanic system of Iceland-Map-en.svg Iceland: Lava from the Katla and the Hekla volcanic systems result in transitional alkalic basalts and the central volcanos ones result in tholeiitic basalts. Question: Is transitional alkalic basalts the same as high alumina basalt? Thx for an answer :) --Chris.urs-o (talk) 19:36, 2 April 2010 (UTC)

Don't you just love scientific terminology. I had a look at this when the question was raised elsewhere (I can't remember either where that was or whether I got round to replying (apparently the answers are by you at Talk:Basalt and no)). From what I gathered, they were considered by some to be the same but not by everyone, which isn't very helpful. Transitional I take to mean transitional between tholeiitic and alkaline. High alumina basalt was a term introduced by Kuno,[1] who interpreted them to be primary melts of mantle material at depths intermediate between those at which tholeiite and alk-basalt magmas were formed. Others have reckoned that they are more likely to be a result of differentiation of a primary magma at depth. Brody & Marsh reckon that they are primary melts, but of quartz-eclogite from the subducting slab - they also point out that it has been shown experimentally that the High-Al basalts can never have been in equilibrium with either an olivine-bearing magma or source rock. I think that this was where I gave up last time :-). This more recent note by Draper [2], does at least define High-Al basalts as aluminium rich tholeiites (which others would probably call transitional I'm guessing). I just found another ref that suggests that some HAB magmas originate by partial melting at the base of continental crust above a mantle upwelling in a rift setting (I have full text access for this one, unfortunately the abstract doesn't go into any detail). I'm not sure if any of this helps. Cheers, Mikenorton (talk) 11:43, 17 April 2010 (UTC)

Recent changes[edit]

This page has improved a lot in the last week. Looks good now.Rolinator 07:47, 3 November 2006 (UTC)

Small usage fix[edit]

Changed "comprised predominantly of basalt" to "composed predominantly of basalt." A thing is not comprised of its parts; a thing comprises its parts. 21:30, 28 March 2007 (UTC)Stephen Kosciesza

Thanks for taking the time to justify your changes, it is appreciated by those of us who watchlist these articles. The Merriam-Webster Online Dictionary entry for "comprise" has a useful note on usage. Based on the note, it would appear that "comprised" is commonly used in this sense, although likely to be criticized as wrong by many (like you). I'm OK with using "comprise" that way, I see it all the time in scientific papers, but I'm happy to accept "composed" as more correct usage.
By the way, you've been making many small but useful conrtributions to Wikipedia over the past months, might I recommend signing up for an acount? See WP:ACCOUNT for info on the numerous benefits of having an account. No pressure, it's up to you. Thanks. --Seattle Skier (talk) 23:01, 28 March 2007 (UTC)

Just a point that this article states that Boninite is usually found in back-arc basins. It should be FORE-ARC basins and it forms when the arc is closer to the subduction zone —Preceding unsigned comment added by (talk) 11:16, 16 November 2010 (UTC)

Extremely confusing[edit]

I'm trying to do a project on basalt and I hardly know what's being said. Some of us are still in high school, you know. BlackSlivers 00:08, 20 June 2007 (UTC)

The following sentence seems awkard to me: Pliny used the word basalt and it is said to have had an Ethiopian origin, meaning a black stone. Even though Pliny has a link, the author uses the name as if anyone reading this article is sure to know who Pliny is and why he was important. I feel it should have had some kind of comment appended to it such as: Pliny, the world's oldest rock hound in the 1920's,................. I humbly submint this comment for peer review and suggest it only in the hope that it will make the article more easliy readabale. No malice was intended. 04:53, 21 September 2007 (UTC)ID 2007-09-21

What about it's uses?[edit]

Don't get me wrong, I like to read about how the stone is formed. But I guess I feel like this article overlooks the practical uses of basalt as tile. I'd fix it myself, but I'm horrible at gathering information in an easy to read way. But it'd be nice to have a section about the various uses of basalt, as well as it's weaknesses/strengths as a material. —Preceding unsigned comment added by (talk) 03:37, 18 September 2007 (UTC)

Whats it used for? found on mars? who cares.. —Preceding unsigned comment added by (talk) 03:06, 19 September 2007 (UTC)

Basalts' Uses[edit]

I also agree with the previous comment about the fact that the artical needs a section about the rocks' uses. I'm currently doing a project on Rocks for school & I've chosen Basalt as one of my subjects. I have been asked to find out about its formation, uses & where its found. However, I cant complete the 'uses' section because of this. I have tried looking for it over the internet & Im sure that it will take me ages to do! So please could you include a uses section in the future - thanks. - Mrsir2 —Preceding unsigned comment added by (talk) 14:29, 6 October 2007 (UTC)


"Traprock" forwards to this article. Could someone add (in the article) why? Thanks, Ibn Battuta (talk) 21:37, 9 December 2007 (UTC)

I've changed it to redirect to trap rock instead. -- Avenue (talk) 09:06, 18 March 2008 (UTC)

What is being said?[edit]

Basalt is an extrusive igneous rock -- this means that Basalt is one member of a class of objects. What distinguishes basalt from the other members of this class? Are no other rocks extrusive and igneous? I have no idea what is being said, and I am not in high school, I am merely a high school science teacher. Billt4 (talk) 01:33, 14 June 2008 (UTC) —Preceding unsigned comment added by Billt4 (talkcontribs) 21:29, 13 June 2008 (UTC)

More data needed[edit]

How about information on the rock, like (average) density (and comparison with that of granite, for example), and hardness. Average crystal sizes of various forms of basalt would be interesting.

I also would be highly interested in (human) uses of basalt. Again, comparison with stones with which most people are familiar (granite, marble) would be helpful.

JKeck (talk) 05:10, 10 July 2008 (UTC)

This page should also include the average chemical composition of basalt, similar to the page on granite.Cadwallader (talk) 18:25, 1 February 2009 (UTC)

ALSO -- I don't believe that the Columbia Basin Basalts extend to Yellowstone National Park as the picture indicates. The Columbia Basalts don't cross the Continental Divide. The pictures of columnar jointing are weak -- try using Google to find some nice shots from the Columbia Basin. Why not add photos of the Deccan Traps and Siberian Traps, too -- the three known places of fissure volcanism.

To answer questions -- average density? Denser than most rocks, including granite. Hardness -- comperable to Mohs? I'd guess an 8. Uses of Basalt? Try googling basalt waste isolation project. Or google "leverite" -- where you just "leave 'er right there." Many uses include aesthetics because of striking jointing. Just a run of the "mil" scientist here, so take very little for what it's worth.

--Moved an edit into Chronological order. --Ancheta Wis (talk) 18:37, 26 January 2009 (UTC)

Commom uses[edit]

Common uses included per request. Making this part of the WikiProject Geology should help revamp this article and make it more practible. Eighthcreek (talk) 03:32, 6 February 2009 (UTC)

Columnar Basalt and Trap Rock quite different[edit]

I, for one, would like to see an article for trap rock kept separate from basalt in general. For one, not all trap rock is basalt, let alone columnar basalt. Trap rock is manifest in three forms: basalt (which is usually extrusive), diabase (which is always intrusive), and hornfels (which can be formed at the surface or in an intrusive setting). Additionally, trap rock can exhibit any of the following qualities: stacked, jointed, or columnar.

In a nut shull, 'trap rock' is just another way of describing most blocky volcanic rocks. It has particular relevance to quarrying since trap rock in its varying forms is crushed to make road and railroad beds. lithium6ion (talk) 22:07, 9 August 2009 (UTC)

Hexagonal Columns[edit]

What is this line supposed to mean: "These structures are often erroneously described as being predominantly hexagonal. In reality, the mean number of sides of all the columns in such a structure is indeed six (by geometrical definition), but polygons with three to twelve or more sides can be observed" - does someone have a different definition of "predominantly" than I do? They're described as being predominantly hexagonal because most of them are hexagonal. Also, what's this about "the mean number [...] is indeed six (by geometrical definition)." How does 'geometrical definition' dictate that it has to be six? It could easily be four, or three. It's six because of the physical process and the physical properties of the material. (talk) 02:44, 29 July 2012 (UTC)

I agree - that's weird, so I fixed it. Jon (talk) 04:09, 29 July 2012 (UTC)

Hacked with Sex[edit]

Something somewhere has been hacked to add the emboldened text to this page's entry. Don't have sufficient Wiki-Fu to do more than bring it to your attention. -- (talk) 04:32, 4 October 2012 (UTC)

Basalt which erupts under open air (that is, subaerially) forms three distinct types of lava or volcanic deposits: scoria; ash or cinder (breccia); and lava flows and then whenever people go in there they get have burned and then when they are having sex its weaker sex.

Odd as that was zapped within a minute of its addition by cluebot hours before your post. Vsmith (talk) 13:23, 4 October 2012 (UTC)
Remember to assume good faith. Dentren | Talk 18:07, 7 May 2013 (UTC)

Higher Resolution Image Available[edit]

Hi all,

This image has come to my attention:

If I can obtain permission from the photographer (which appears to be this Simon Ward) to use this image, should it be used here? (Asking as I am not sure whether this image is as appropriate as I think it is, and would like second opinions)

Ultimately I am seeking to see whether it would be suitable to replace the current image of Columnar Basalt,

Thanks all! HHP2K (talk) 15:21, 6 May 2013 (UTC)

In my personal opinion images shouldn't be watermarked on Wikipedia. The author of the image gets all the credit when his image is viewed full screen or on Commons. Otherwise we might as well wait until the next Wikipedian visits that outcrop. --Tobias1984 (talk) 18:50, 6 May 2013 (UTC)
Its a good picture except for the watermark/signature in the corner. Agree with Tobias1984 that "images shouldn't be watermarked on Wikipedia" Dentren | Talk 00:55, 7 May 2013 (UTC)
Yes, good replacement choice, if, as others suggest, you can get him to submit it without the water mark. - (talk) 03:33, 7 May 2013 (UTC)

Silica content[edit]

Could someone help me with this. At the beginning of the article it says that Basalt contains less than 20% Quartz.In the drop down menus at the foot of the page it says that Basalt is Mafic and has a 45 to 52% SiO2 content is this because the Si O2 in the Feldspar etc is included. — Preceding unsigned comment added by Ruskin (talkcontribs) 09:58, 9 June 2013 (UTC)

One way of expressing the chemical composition of a rock is to list it as percentages of separate oxides. The difference that you noted is because the total SiO2 content of a basalt includes contributions from all the silicates, particularly feldspar, olivine, amphiboles and pyroxenes. Mikenorton (talk) 10:34, 9 June 2013 (UTC)
Also the 20 % Quartz are volume (this example 20 cm³ / 100 cm³) and the 45 to 52 % SiO2 are mass (45 to 52 g / 100 g) --Tobias1984 (talk) 14:50, 9 June 2013 (UTC)

Thanks for the info. — Preceding unsigned comment added by Ruskin (talkcontribs) 19:45, 9 June 2013 (UTC)

Possible typo at the end of the "Petrology" section[edit]

At the end of the petrology section we have - "The origin of high-alumina basalt continues to be controversial, with interpretations that it is a primary melt and that instead it is derived from other basalt types (e.g., Ozerov, 2000)."

Should that read "it is not a primary melt" (or similar wording) ? In fact the whole sentence could probably do to be reworded if I'm interpreting it correctly ...— Preceding unsigned comment added by ManyMore (talkcontribs) 13:31, 1 November 2015

Thanks for pointing this out. It is clear from Ozerov 2000 that this needs to be rephrased. I have updated the para accordingly and link the reference to a callout. --Mirokado (talk) 14:30, 1 November 2015 (UTC)

Thanks for the update. Good rewording by the way. ManyMore (talk) 23:57, 1 November 2015 (UTC)

Basalt types[edit]

In the "Types" section MORB is separated from tholeiitic basalt. I find this confusing as MORB is a type of tholeiitic basalt, albeit one errupted in a very particular place.

A bit of reworking of this section would probably help to make things a lot clearer! Perhaps delete the MORB paragraph and add the following to the end of the tholeiitic paragraph -

   Ocean floor basalts, errupted originally at mid-ocean ocean ridges, are known as MORB (Mid-Ocean Ridge Basalt) and are characteristically low in incompatible elements. 

The mention of EMORB and NMORB could be moved to the "Geochemistry" section, and perhaps expanded on?

And at the moment, MORB links to a mid-ocean ridge page, which doesn't seem right as MORB is mentioned there at all! We should certainly link mid-ocean ridge there, but MORB, I suggest, needs to link to somewhere else.

ManyMore (talk) 10:58, 3 November 2015 (UTC)

Reorganized a bit and did some fixing. Demoted the jargony acronymisms a bit. Vsmith (talk) 14:25, 3 November 2015 (UTC)

OK, that reads a lot better, thanks. I've found that I'm now able to edit the Basalt page - couldn't yesterday! Did playing around on my own Sandbox page really get me enough "credit" to allow me to edit a semi-protected page??? I'll look at making more changes when I get a free moment - certainly the last line of the "Definition" section "so much so that there is an alternate (but less well known) name for this kind of basalt" needs tweaking! I assume the reference is to Komatiite? I might even add a new page on some (geological) subject some day! ManyMore (talk) 16:13, 3 November 2015 (UTC)

I recomend you strongly to translate the article from the well-referenced Spanish es:basalto, which anyways uses almost only English language sources. Sietecolores (talk) 07:50, 4 November 2015 (UTC)

Rework of the Basalt article[edit]

Sietecolores has suggested using a translation of the Spanish Wikipedia version of Basalt (es:basalto). I'm not sure, Sietecolores, if you mean a complete replacement of the English version with the (translated) Spanish version, or whether you are thinking we could just use parts of the Spanish article?

I don't speak Spanish, but just having had a very quick look at the Spanish page I see that it describes Olivine and Plagioclase as "essential" minerals (in a basalt) and augite (a pyroxene) as an accessory mineral. I'm not sure I agree with that!

I haven't read the rest of the article, though I'll ask my other half to translate it for me when she gets time (she's doing a foreign languages degree, "majoring" in French and Spanish).

ManyMore (talk) 17:33, 4 November 2015 (UTC)

The Spanish version is shorter, but better sourced - and many of the sources are in English. I have imported their reading list. It wouldn't make sense to simply replace the English article, but its quality could be improved. RockMagnetist(talk) 19:03, 4 November 2015 (UTC)
I have nowhere said anything on how much of the article could be expanded with material from the Spanish wikipedia. But clearly the current poorly sourced version is not trustwothy, and trusworthyness is one of the main problems of Wikipedia. This article have had these problems for years. I would be glad to see things going on here. Regarding essentials minerals clearly olivine and plagioclase are key to identify basalt in the field or under the microscope, and this has been known and used before and after the IUGS recomended the TAS digram approach. Of course as with most volcanic rock essential minerals might be absent if the rock aphyric, but this does not disqualify olivine and plagioclase from being essential minerals (in the identification of the rock). Sietecolores (talk) 20:19, 6 November 2015 (UTC)
Isn't it plagioclase and pyroxene that are the essential minerals in a basalt, and olivine that's an accessory (though a common one, and sometime abundant as in an olivine basalt). Describing pyroxene as an accessory is just wrong, isn't it? ManyMore (talk) 11:20, 9 November 2015 (UTC)
The relative proportions of plagioclase and olivine is what is used to estimate if a dark volcanic rock is a basalt or an andesite (in the lack of TAS). If olivine is lacking the rock is most likely an andesite/basaltic andesite. So olivine is key to identify basalts in field or under the microscope. Then either clinopyroxene or plagioclase can follow in the Bowen series, usually plagioclase is the most abundant. Sietecolores (talk) 08:53, 11 November 2015 (UTC)

Pillow basalts[edit]

This section in the article is treated as if pillow basalts are limited only to submarine eruptions, which is false. Pillow basalts also form when basaltic lava erupts under glacial ice and are thus found at tuyas and subglacial mounds. I don't have time to make adjustments in the article I just wanted to point this out. Volcanoguy 09:12, 16 December 2015 (UTC)

Thanks for raising this point. I've added a sentence to this article, which at least ends its ommission. GeoWriter (talk) 17:23, 16 December 2015 (UTC)
And yet another possibility is lava flowing or erupting into a lake. Volcanoguy 13:26, 20 December 2015 (UTC)
They can also form when lava flows into a river. So pillow basalts can form during submarine, subglacial, subaqueous and subaerial eruptions. Volcanoguy 14:30, 20 December 2015 (UTC)