Platinum (Pt) is one of the rarest elements on Earth. Only 190 - 200 tons of platinum are mined each year versus 2500 - 3300 tons of gold. When you add in the fact that 14 tons of raw material must be used to produce 1 measly ounce of pure platinum, and it takes 50 different steps to extract it from its ore, you can see why it costs so much. Only 20% of the world's supply of platinum goes into jewelry and watches. Because platinum does not oxidize, is insoluble in hydrochloric & nitric acid, and has an extremely high melting point of 1772˚C there are many industrial applications for it. 70% goes into catalytic converters for automobiles. The remaining 10% is used in varying items like pacemakers, cancer medications, iPods, fuel nozzles in jet engines, and even missile nose cones. When alloyed with cobalt it can be made into a powerful magnet. platinum ore nugget: Platinum is part of a group of elements including rhodium, palladium, iridium, osmium, and ruthenium called Platinum Group Metals. When the Spaniards came across it in South America in the early 1700's they called it platina meaning "little silver". The pre-Columbian Indians had previously used it for centuries. King Louis XV of France declared it the only metal fit for a king because of its scarcity. Today it is mined in Columbia & Peru, the Ural Mountains of Russia, Western Canada & the Northwestern US, and South Africa. Occasionally it is a welcome byproduct of nickel ore processing in Ontario. Platinum is a prized material for watch cases since it doesn't stain or tarnish. It also has a beautiful silvery white color that doesn't require plating. It has incredible durability - if you scratch it, the metal is only displaced like a dent; it isn't removed off the case. Platinum alloys are 95% pure (.950) compared to the 75% purity (.750) of 18K gold or 58.5% purity (.585) of 14K gold or even the 92.5% purity (.925) of most silver jewelry. Of course there are other factors that make a platinum watch expensive. Special polycrystalline tools are needed since it is the hardest of all precious metals and would break the tools used to produce gold cases. Platinum also requires slower milling speeds and lower pressure to minimize friction which would cause the surface to "orange peel" or stipple. Juan-Carlos Torres, CEO of Vacheron Constantin, told WatchTime magazine "you just look at a platinum dial and you ruin it". He estimates that "you have to work on 500 platinum dials to get 150 right." It can take 5 times longer to make a platinum dial than a gold one, and 3 times longer to produce a platinum case over a gold case. As stratospheric as the price of platinum can be, it is still highly sought after. The U.S. is the biggest market, accounting for 23% of world-wide sales. Almost 3/4 of platinum watches made sell for $25,000 or more and over 2 dozen brands offer products made with the metal. * photo & quote credits to WatchTime magazine
As you note, in addition to its desirability as an ornamental metal, platinum is rare and has important technological applications. It should be valuable. Growing up, I always thought of platinum as being a level above gold in "preciousness". If you got a credit card, the lowest level was silver, gold was the next step up, and a platinum card was the top of the line. Then a funny thing happened in the 70s and 80s. the value of platinum plummeted relative to gold, and continued to fluctuate wildly. Since 2015, platinum has been consistently cheaper than gold. Many people are surprised to hear that the current spot price of platinum is only 70% of that of gold. http://www.kitco.com/commentaries/2017-02-07/The-46-Year-Record-of-Platinum-Gold-Ratios.html
Platinum is usually alloyed with either palladium, or iridium, in the formation of jewellery. Such jewellery items will usually be marked plat/irid, or plat/pal. Platinum usually comprises 95z of the alloy. Rhodium (I understand) is the costliest metal of the platinum group. Check the price chart above, and compare the prices to rhodium at $2,240.00 (U S) per ounce! Ruthenium and osmium are not used in making jewellery. If you have ever noticed the notation “osmium stylus” on a phonograph needle, this was a popular use for osmium, because of its hardness. Better phonograph needles may be tipped with diamond.