All four of these are the densest (highest "specific gravity") materials found (not counting the radioactive elements). All but Re are "Platinum Group" metals, all four share pretty similar chemical characteristics. Here is a quick look at the densities and prices of these four metals:
Atomic
|
Density
|
Price
|
|
Metal
|
Number
|
(gm / cc)
|
($ / toz)
|
Rhenium
|
75
|
21.02
|
$110
|
Osmium
|
76
|
22.59
|
$400
|
Iridium
|
77
|
22.56
|
$710
|
Platinum
|
78
|
21.45
|
$1,450
|
Notes:
1) Rhenium is available by the kilo, and has large price differences depending on form.
2) Iridium has large price differences depending on form.
3) Platinum price is as of today.
I would like to note that the above are heavier by a pretty good margin versus other metals, I believe gold is next at 19.30 gm / cc and tungsten at 19.25 gm / cc. Depleted uranium (U-238) weighs in at about 19.05 gm / cc, but is radioactive (and so could be easily detected with Geiger counters and other detection equipment).
Platinum would be about 8% heavier than tungsten or depleted uranium, a good caliper and scale would be sufficient to tell Pt from W or U.
Rhenium is not a "Platinum Group" metal, but does lie adjacent to osmium on the Periodic Chart, and it also is rare, expensive and sought after (by some industrial users).
The other "Platinum Group" metals (palladium, rhodium and ruthenium) are considerably less dense (around 12 gm / cc, relatively close to silver and lead), and so are not examined in this article.
Each of these metals are discussed in nice articles at wikipedia.org. ALL of the chemical elements are discussed there in separate articles, and wiki is the place to start for further research.
* * *
Platinum, of course, is by far the most familiar of these four heaviest metals. A number of nations make Pt bullion coins (including the US Mint, which started making the Platinum Eagles again in 2014 due to investor interest). Although Pt coins are not as popular as gold and silver ones, they can be found at larger coin shops. Platinum would be the "third" precious metal for small investors interested in this kind of hard assets. The price spreads are not too high for platinum, meaning that they are relatively easy to buy and sell, particularly the Platinum Eagle (here in the USA). The Pt Eagles do however, command a premium (perhaps $100 per 1 oz coin) over other coins, but you would "get that premium back" upon selling (similar to buying and selling Silver Eagles here in America).
Of the four metals examined in this article, platinum would definitely be the one to start with if you own none of them yet. Platinum is reasonably familiar to those who deal in precious metals, the price, while expensive, would not differ substantially from "wholesale" prices (which are a problem with the other three metals, as discussed below).
Platinum is used in catalysts (both car engine catalytic converters as well as in chemical & refineries) and is used in jewelry (diamond mountings in rings and even as platinum jewelry itself -- particularly in China). While used in jewelry, many jewelers (small ones, say) find platinum to be hard to work with, as it is hard and has a high melting point vs. gold and silver. But, silver is too weak to be used in mounting expensive diamonds.
Platinum was even used as a genuine circulating currency (in Russia in the 1800s for a while), in the unusual denominations of three, six and 12 rubles. Here is a picture of a Russian Three Ruble coin from 1828 (image from coinshome.net):
These Russian coins are extremely rare, one of my friends sent me an eBay link a year or so ago offering a six ruble coin for $19,000... These platinum coins, of course, are for numismatists and other specialized coin collectors.
* * *
Osmium I have covered before, I bought a 1 troy ounce pellet (blob) from elementsales.com some time ago. Os is said to have a blueish tint, and mine does, see the photo:
That little tiny blob weighs 1 troy ounce (about 31 gm).
Osmium is very hard and the densest (stable) material in the universe! So, one would think that it would be a "must have" for everyone interested in materials. Yes, well, OK it is kind-of cool, but Os reacts (slightly in blob form, much more so in powder form) to form TOXIC osmium tetroxide... So, even though it is so rare, heavy and hard, well, I do not think it is a good "investment". Apparently only some 2000 ounces are used in the USA each year, and the USGS (last I heard) does not even track its production.
* * *
Iridium is just barely behind osmium in density, hardness and rarity. But, iridium has more industrial applications. Like the other Platinum Group metals, it is used as a catalyst and is used in more applications than osmium. Iridium apparently has a slight yellow tint (as osmium has a slight blue one).
Wikipedia's article mentions that iridium is used as a source of antiprotons (a form of antimatter).
Iridium, you may also recall, is the metal found in over 100 outcrops all over the world that marks the "K-T Boundary" (now officially called the Cretaceous-Paleogene Boundary), it is thought that this layer is remains of a meteorite that hit the Yucatan some 65,000,000 years ago, killing off the dinosaurs. Iridium is much more common in meteorites than in rocks from the earth's crust.
Iridium powder (similar to what I recently bought) apparently is used to make the darkest black colorant in adding color to porcelains.
I was told by my iridium vendor (http://preciousmetalpurchase.com/metals/iridium/) that powder is the most usual way iridium is sold to (and used by) industry. This source of iridium offered the one ounce to me for $709, where elementsales.com wants $980 plus shipping). On the other hand, I have dark gray / black powder vs. a cool looking pellet.
Iridium is much less toxic than osmium, but as a powder it can react and burn in air (like so many other powders).
http://www.rwmmint.com/products/iridium has cut its price of 1 oz of iridium (to $1495 for their 1 toz ingot, I have their picture from my recent article: http://robertmixblog.blogspot.com/2014/08/50-bills-iridium-bitcoin-app-for-iphone.html. That is still more than what I want to pay though...
* * *
Rhenium is available from http://www.rwmmint.com/products/rhenium for $269 per toz, here is their picture of their ingot:
I believe that investors may be able to get a better deal on rhenium from Lipmann Walton and Co., Ltd. (of the UK), I am waiting on price and/or availability (they might only quote by the kilo however), their website is very interesting to anyone likes chemistry or materials science: http://www.lipmann.co.uk/metals-traded/. Lipmann Walton buys rhenium from places like Kazakhstan, and then sends it off to metals refiner Heraeus of Germany to make it at least 99.9% pure.
A price I just saw (I do not know how current) is about an average of $3500 per kg (not toz), or some $105 - $110 in round numbers per toz: http://www.metalprices.com/metal/rhenium/rhenium-metal-99-9-na
Rhenium has one very interesting application that any prospective investors might want to know about: it is used in current "superalloy" third generation (newest jet engines, like used in the Boeing 787 "Dreamliner" or the engines in the new US F-35 jet fighter) jet engine turbine-blades. Rhenium superalloy provides better performance at some 50 degrees C than current alloys. And there are no substitutes, an engine maker wants higher performing engines, they MUST use up to 6% rhenium. For each turbine blade...
See the below cool picture from wikipedia's article on rhenium (this is Pratt & Whitney's F-100 engine):
Rhenium is extremely rare, platinum is 10 times more common. Only about 50 metric tons (50,000 kg) are produced each year. It is typically produced from molybdenum residues, it is a "by-product of a by-product" (from copper mines, especially Chile).
Apparently rhenium is of low toxicity.
* * *
OK, so all four of these "heaviest metals" are sufficiently dense vs. tungsten (or uranium) to be detected relatively easily. So, if you have money left over from buying gold and silver, here would be my suggestions on investing in this "micro-sector":
1) The obvious place to start would be platinum. Platinum coins are produced by a number of mints, and are not really all that scarce. Platinum is useful to industry (where gold has relatively minor applications). Platinum is fairly easily recognized, and is liquid (an important consideration if you must sell it).
2) IMO, if you could get it a good price, rhenium looks to be a pretty good "speculation in physical metal". I really like that non-substitutable nature of its use in jet engine turbine blades, that bodes well for the demand of this metal going into the future. If the future is going to be good (like we all hope, yet worry that it may not be), then rhenium looks promising.
3) In third place is iridium. This is easier to get than osmium, is not toxic, and has more applications. I have not completed my research into iridium. Perhaps by buying in large lots (say 100 toz or more), the prices might be more reasonable.
4) Osmium, alas, is really only for hobbyists or if you "just want it" (and there are plenty of people who "want" stuff like that). Osmium does have the bragging rights as to being the earth's scarcest metal and the densest. Too bad it is toxic. But, what do you want for only $400 (or so) per ounce?
