My periodic table poster is now available! Potassium is an alkali metal, more reactive than sodium, but otherwise fairly similar both in pure form and in how it forms compounds. It's similar enough that potassium chloride serves as a substitute for sodium chloride, table salt, in foods intended for people who are on a low sodium diet. Surprisingly, it's less dense than sodium even though it's lower down in the periodic table: More often than not lower elements are heavier because they contain more protons and neutrons in their nuclei. But working against this is the fact that the increased nuclear charge tends to pull all the electrons closer, resulting in a smaller atomic radius and hence a higher density. In the sodium/potassium pair this effect counteracts the effect of increased nuclear mass. (Thanks to reader Chris Hamilton for pointing out that in an earlier version of this description I actually said potassium was heavier than sodium: So common is the trend I didn't even look at the actual densities before writing that.) Potassium plays many important roles in the chemical processes of life, including nerve impulse transmission. In all such situations, the potassium is in the form of K- ions, not elemental potassium. Like all alkali metals, potassium metal itself doesn't last long in the real world, reacting quickly with water or just moisture in the air to form potassium hydroxide and hydrogen gas (which then explodes). Compare at other websites: periodictable.com Wikipedia WebElements Museum Display Minerals Translations and Etymology Science Fiction (Main Site) Comics Collections: Elements in the Human Body Minerals, Alloys, and Compounds Elements that spell OLiVEr SAcKS Elements Popular in Collections Poster Samples Samples with Rotatable Images Samples with High Resolution Spin Movies Salt substitute. People who are supposed to restrict their sodium intake for health reasons can use potassium chloride instead of sodium chloride (salt) for seasoning. Potassium chloride is sold in every grocery store as one or another brand of "NoSalt", "Diet Salt", etc. Some are a blend of sodium and potassium chlorides, others like this one are nearly pure potassium chloride and/or other potassium salts. This is by and large a good thing. As a reader, Phil Karn, has pointed out, potassium is a necessary nutrient, and for people with high blood pressure displacing sodium with potassium is an important step towards reducing it. But interestingly, naturally occurring potassium contains a small but measurable fraction of potassium-40, which is radioactive. I bought a container of it expecting it to register barely, if at all, on our Geiger counter. Instead it is really quite unmistakable: A plate with about 4 tablespoons spread out registers over 400 counts per minute. Of course, one normally wouldn't eat that much at a time: Using a few assumptions about how much people might eat, I would guesstimate that steady use might result it doubling the average amount of background radiation you're normally exposed to. This is not significant considering that just living in certain cities, near a granite building, etc, will more than double the average background level. Interestingly, I have learned from Phil Karn that Issac Asimov long ago made a similar calculation: That the radiation dose from potassium in the body is roughly equal to the radiation dose from the other natural sources put together. This website has an interesting speculation about the role of potassium's radioactivity. If you're currently using a salt substitute, please don't stop because of this information! The risk from radiation is utterly insignificant compared to the risk from high blood pressure. Furthermore, the amount of potassium in your body is probably about the same from day to day regardless of whether you're eating salt substitute or not. This is because the body needs a certain amount, and generally gets more than it needs in food whether you are using salt substitute or not: The excess is excreted efficiently. Nevertheless, I'm keeping it in our Hot Box just for fun. It's a great demonstration of the importance of location: Outside the Hot Box it's just a container of salt, inside the Hot Box it's a real conversation piece. There is a lot of interesting information about the surprising places you can find radiation in this book. Source: Grocery Store Contributor: Theodore Gray Acquired: 27 August, 2002 Text Updated: 11 August, 2007 Price: $6 Size: 6" Purity: 52% Sample Group: Medical Small rod. Potassium is really not that hard to get, nor is it very expensive. But for some reason I just didn't have any for the longest time, until the very kind Max Whitby of the The Red Green & Blue Company put me out of my misery by sending me a sample from the element collection his company sells. They sell a very nice element collection in several versions. Max Whitby, the director of the company, very kindly donated a complete set to the periodic table table. To learn more about the set you can visit my page about element collecting for a general description or the company's website which includes many photographs and pricing details. I have two photographs of each sample from the set: One taken by me and one from the company. You can see photographs of all the samples displayed in a periodic table format: my pictures or their pictures. Or you can see both side-by-side with bigger pictures in numerical order. The picture on the left was taken by me. Here is the company's version (there is some variation between sets, so the pictures sometimes show different variations of the samples): Source: Max Whitby of RGB Contributor: Max Whitby of RGB Acquired: 25 January, 2003 Text Updated: 11 August, 2007 Price: Donated Size: 0.5" Purity: 99.5% Sample from the Everest Set. Up until the early 1990's a company in Russia sold a periodic table collection with element samples. At some point their American distributor sold off the remaining stock to a man who is now selling them on eBay. The samples (except gases) weigh about 0.25 grams each, and the whole set comes in a very nice wooden box with a printed periodic table in the lid. To learn more about the set you can visit my page about element collecting for a general description and information about how to buy one, or you can see photographs of all the samples from the set displayed on my website in a periodic table layout or with bigger pictures in numerical order. Source: Rob Accurso Contributor: Rob Accurso Acquired: 7 February, 2003 Text Updated: 29 January, 2009 Price: Donated Size: 0.2" Purity: >99% Chunks under argon. I love it when someone says my sample of a certain element sucks, because it's usually a prelude to them telling me that I should have the much better version then could send me, if I'm interested. Greg, bless his heart, thought a lot of my samples suck. He sells lots of very nice and very unusual elements on eBay and elsewhere: Check the Source link for details. The potassium in these sealed vials is very shiny: Hopefully they will stay that way for a good long time. The 3D version came out quite nicely: I was able to use my fiber optic illumination system to make the glass nearly invisible. Taking the samples out to photograph them would have been possible only in an argon glove box, or they would have oxidized very quickly. Source: Greg P Contributor: Greg P Acquired: 18 April, 2003 Price: Donated Size: 1" Purity: 99.9% Molten blobs under argon. Ampouling potassium in a clean and dry enough environment to keep it shiny is quite difficult: It is an extremely reactive metal to say the least. This sample demonstrates great skill in its ampouling, especially since it was done using only "the simplest methods", according to the source. Source: Frank Liebscher Contributor: Frank Liebscher Acquired: 28 January, 2004 Price: Donated Size: 3" Purity: 99.9% Cut cubes under oil. This is a sample I prepared specifically for a film project, to make a 360-frame rotation image. It's scrap potassium from my anonymous sodium supplier, carefully cut up under oil to reveal shiny surfaces. When absolutely fresh, the surface is bright silver, but as you can see from the pictures this sample has turned slightly bluish. I could have worked harder to prevent this, but actually the blue cast is somewhat attractive in the photographs, and it is quite characteristic of the early stages of potassium oxidation. This helps to differentiate it visually from sodium, which would otherwise look identical. OK, I'm just rationalizing, I was too lazy and didn't have the right set up handy to create a really shiny sample, so I settled from this one. Still, it looks quite pretty, nicer I think than a silvery sample would. I chose this sample to represent its element in my Photographic Periodic Table Poster. The sample photograph includes text exactly as it appears in the poster, which you are encouraged to buy a copy of. Source: Anonymous Contributor: Anonymous Acquired: 12 May, 2005 Text Updated: 8 December, 2007 Price: Donated Size: 1" Purity: 99.9% Banana. Bananas are known for being high in potassium, which makes them slightly more radioactive than the average food (because some naturally occurring potassium is the radioactive potassium-40 isotope). Source: Walmart Contributor: Theodore Gray Acquired: 8 April, 2009 Text Updated: 9 April, 2009 Price: $0.50 Size: 7" Purity: 0.36% Super-clean potassium. You are just never going to see cleaner potassium than this. It is almost impossible to ampule potassium without at least a tiny bit of oxidation, but this 225g ampule is absolutely, totally clean. Unfortunately it's not mine, it was just borrowed for photography. Source: Anonymous Contributor: Anonymous Acquired: 17 April, 2009 Text Updated: 17 April, 2009 Price: None Size: 2" Purity: >99.9% Lepidolite from Jensan Set. This sample represents lithium in the "The Grand Tour of the Periodic Table" mineral collection from Jensan Scientifics. Visit my page about element collecting for a general description, or see photographs of all the samples from the set in a periodic table layout or with bigger pictures in numerical order. Source: Jensan Scientifics Contributor: Jensan Scientifics Acquired: 17 March, 2003 Price: Donated Size: 1" Composition: K(Li,Al)3(Si,Al)4O10(F,OH)2 Apophyllite from Jensan Set. This sample represents oxygen in the "The Grand Tour of the Periodic Table" mineral collection from Jensan Scientifics. Visit my page about element collecting for a general description, or see photographs of all the samples from the set in a periodic table layout or with bigger pictures in numerical order. Source: Jensan Scientifics Contributor: Jensan Scientifics Acquired: 17 March, 2003 Price: Donated Size: 1" Composition: KCa4Si8O20(F,OH).8H2O + KCa4Si8O20(OH,F).8H2O Sylvite from Jensan Set. This sample represents potassium in the "The Grand Tour of the Periodic Table" mineral collection from Jensan Scientifics. Visit my page about element collecting for a general description, or see photographs of all the samples from the set in a periodic table layout or with bigger pictures in numerical order. Source: Jensan Scientifics Contributor: Jensan Scientifics Acquired: 17 March, 2003 Price: Donated Size: 1" Composition: KCl Boltwoodite. I think it's the yellow crystals on this rock that are the actual Boltwoodite: I have no idea what the rest is. Source: SoCal (Nevada), Inc Contributor: Theodore Gray Acquired: 3 June, 2005 Price: $28 Size: 1.5" Composition: (K+Na)[(UO2)(SiO3OH)](H2O)1.5 Carnotite. The yellow crust is the carnotite, an ore of uranium that also contains some traces of radium, which is used to justify the name "Radium Ore Revigator" used to describe the water jug you'll find listed under uranium (and which is lined with carnotite). Source: eBay seller dr**zarkoff Contributor: Theodore Gray Acquired: 3 June, 2005 Price: $15 Size: 1.5" Composition: K2(UO2)2(VO4)2.3H2O Zippeite. I think most of this rock is actual zippeite, but I don't know for sure. Source: eBay seller dr**zarkoff Contributor: Theodore Gray Acquired: 3 June, 2005 Price: $20 Size: 1.5" Composition: K4(UO2)6(SO4)3(OH)10.4H2O Alunite. Description from the source: Alunite (KAl3(SO4)2(OH)6 trig.), La Tolfa, Civitavecchia, Lazio, Italy. Small crystal clusters on the same massive material from a classic italian locale. 3,8x2,2x1,5; 22 g. Source: Simone Citon Contributor: John Gray Acquired: 26 September, 2008 Text Updated: 28 September, 2008 Price: Trade Size: 1.5" Composition: KAl3(SO4)2(OH)6 Orthoclase. Description from the source: Orthoclase (K Al Si3 O8 mon.), San Gotthard, Tessin, Switzerland. Geminated crystals of the variety Adular. 5x4x3 cm; 25 g. Source: Simone Citon Contributor: John Gray Acquired: 30 September, 2008 Text Updated: 1 October, 2008 Price: Trade Size: 2" Composition: KAlSi3O8 Londonite-Rhodizite. Description from the source: Londonite-Rhodizite serie ( (Cs K Rb) Al4 Be4 (B Be)12 028 to Rb=0 for the pure Rhodizite cub.), Antandrokomby, Antsirabe`, Madagascar. Rich in rubidium example, with Tourmaline (probably Liddicoatite). 3,1x2,5x2 cm; 22 g. Source: Simone Citon Contributor: John Gray Acquired: 30 September, 2008 Text Updated: 1 October, 2008 Price: Trade Size: 1.25" Composition: (CsKRb)Al4Be4(BBe)12028 Photo Card Deck of the Elements. In late 2006 I published a photo periodic table and it's been selling well enough to encourage me to make new products. This one is a particularly neat one: A complete card deck of the elements with one big five-inch (12.7cm) square card for every element. If you like this site and all the pictures on it, you'll love this card deck. And of course if you're wondering what pays for all the pictures and the internet bandwidth to let you look at them, the answer is people buying my posters and cards decks. Hint hint. Source: Theodore Gray Contributor: Theodore Gray Acquired: 19 November, 2008 Text Updated: 21 November, 2008 Price: $35 Size: 5" Composition: HHeLiBeBCNOFNeNaMg AlSiPSClArKCaScTiVCrMn FeCoNiCuZnGaGeAsSeBrKr RbSrYZrNbMoTcRuRhPdAg CdInSnSbTeIXeCsBaLaCePr NdPmSmEuGdTbDyHoErTm YbLuHfTaWReOsIrPtAuHgTl PbBiPoAtRnFrRaAcThPaUNp PuAmCmBkCfEsFmMdNoLrRf DbSgBhHsMtDsRgUubUutUuq UupUuhUusUuo Lepidolite. Description from the source: Lepidolite (K (Li Al)3 (Si Al)4 O10 (F OH)2 mon.), Varutra"sk, Skellefteao, Va"sterbotten, Sweden. Laminar deep purple crystals on matrix. 5x3,5x3 cm; 45 g. Source: Simone Citon Contributor: John Gray Acquired: 19 November, 2008 Text Updated: 20 November, 2008 Price: Trade Size: 2" Composition: K(LiAl)3(SiAl)4O10(FOH)2 Londonite-Rhodizite. Description from the source: Londonite-Rhodizite serie ( (Cs K Rb) Al4 Be4 (B Be)12 028 to Rb=0 for the pure Rhodizite cub.), Antandrokomby, Antsirabe`, Madagascar. Yellow, partially translucent crystals on matrix with tourmaline. I repeat these species also for other elements, but are very interesting and rich in rare elements. 3,5x2,5x1,5 cm; 12 g. Source: Simone Citon Contributor: John Gray Acquired: 19 November, 2008 Text Updated: 20 November, 2008 Price: Trade Size: 1.4" Composition: (CsKRb)Al4Be4(BBe)12 Lepidolite. Description from the source: Lepidolite (K (Li Al)3 (Si Al)4 O10 (F OH)2 mon.), Aracuai`, Minas Gerais, Brazil. Little crystals on clear Quartz. 1,2x0,8x0,8 cm: 1 g. Source: Simone Citon Contributor: John Gray Acquired: 10 January, 2009 Text Updated: 10 January, 2009 Price: Trade Size: 0.5" Composition: K(Li,Al)3(Si,Al)4O10(F,OH)2 Londonite-Rhodizite. Description from the source: Londonite-Rhodizite serie ( (Cs K Rb) Al4 Be4 (B Be)12 028 to Rb=0 for the pure Rhodizite cub.), Antandrokomby, Antsirabe`, Madagascar. Perfect isolated crystals. 1x0,8x0,7 cm the bigger; 2 g all. Source: Simone Citon Contributor: John Gray Acquired: 28 January, 2009 Text Updated: 29 January, 2009 Price: Trade Size: 0.4" Composition: (CsKRb)Al4Be4(BBe)12028 Rock of alum. This is a hunk of potassium alum, used for many things but sold retail in this form primarily as a deodorant. Source: eBay seller saratthasamuccaya Contributor: Theodore Gray Acquired: 8 February, 2009 Text Updated: 8 February, 2009 Price: $6/pound Size: 3" Composition: KAl(SO4)2.12H2O Cooking alum. Powdered alum meant for use in cooking. Source: Walmart Contributor: Nick Mann Acquired: 11 March, 2009 Text Updated: 12 March, 2009 Price: $1 Size: 2" Composition: KAl(SO4)2.12H2O Miserite. Description from the source: Miserite (K (Ca Ce)6 Si8 O22 (OH F)2 tric.), Kipawa Alcalyne Complex, Villedieu Tow., Quebec, Canada. Purple section crystals with granular red Eudyalite and beige Vlasovite. Rich in rare earth elements. 2x1,5x1,5 cm; 6 g. Source: Simone Citon Contributor: John Gray Acquired: 11 March, 2009 Text Updated: 3 April, 2009 Price: Trade Size: 0.75" Composition: K(Ca,Ce)6Si8O22(OH,F)2 Potash fertilizer. An example of a basic potassium fertilizer, this is 6% K2O, or about 5% potassium. Source: eBay seller sunshinehope Contributor: Theodore Gray Acquired: 28 March, 2009 Text Updated: 29 March, 2009 Price: $12 Size: 10" Composition: K2O Sulfate Of Potash. An example of a basic potassium fertilizer, potassium sulfate. Source: eBay seller sunshinehope Contributor: Theodore Gray Acquired: 28 March, 2009 Text Updated: 29 March, 2009 Price: $12 Size: 10" Composition: K2SO4 Mica sheet. This is a sheet of mica, a papery thin mineral that was often used as an electrical insulator. The term mica refers to a range of specific minerals and I don't know which one this is exactly, so the composition is just a guess. Source: Mark Peterson Contributor: Mark Peterson Acquired: 13 January, 2010 Text Updated: 13 January, 2010 Price: Donated Size: 3" Composition: (KLi2Al(Al,Si)3O10(F,OH)2    My periodic table poster is now available!