Precious metals are usually rare, chemically relatively inert, and often colorful.
They are transition metals ruthenium (Ru) through silver (Ag) and rhenium (Re) through gold (Au).
Gold (Au) is the most prestigious metal known, but it's not the most valuable. Gold is the only metal that has a deep, rich, metallic yellow color. Almost all other metals are silvery-colored. Gold is very rare in crustal rocks - it averages about 5 ppb (parts per billion). Where gold has been concentrated, it occurs as wires, dendritic crystals, twisted sheets, octahedral crystals, and variably-shaped nuggets. It most commonly occurs in hydrothermal quartz veins, disseminated in some contact- & hydrothermal-metamorphic rocks, and in placer deposits. Placers are concentrations of heavy minerals in stream gravels or in cracks on bedrock-floored streams. Gold has a high specific gravity (about 19), so it easily accumulates in placer deposits. Its high density allows prospectors to readily collect placer gold by panning.
Platinum can also occur as nuggets such as the one imaged on the right from Russia.
Native silver does occur as cubic, octahedral, or dodecahedral crystals; "also elongated, arborescent, reticulated, or as thin to thick wires."
Native iridium such as the small cubic crystal shown in the image on the right is rare.
The crystal of native osmium shown on the right is about 2 mm across.
"Natural Palladium [like the nugget shown on the right] always contains some Platinum."
This palladium nugget is from Bom Sucesso Creek, Serro, Minas Gerais, Brazil.
"(Pd,Cu) alloys, some with the approximate composition PdCu4, are reported by Kapsiotis et al. (2010)."
The piece of native palladium [image on the left] from the Mednorudyanskoye Cu Deposit, Nizhnii Tagil, Sverdlovskaya Oblast', Middle Urals, Urals Region, Russia, probably contains some copper.
Potarite has the chemical formula PdHg.
On the right is a piece of potarite is from Serro, Minas Gerais, Brazil.
"Native rhenium was first discovered in the Earth's crust in wolframites from a rare metal deposit in the Transbaikal region . [...] The study of the lunar regolith from two sites revealed native rhenium particles with different morphological features: irregular dense particles from Mare Fecunditatis and spheroidal particles from Mare Crisium. The origin of particles (less than 10 µm in size) is assigned to exhalative processes . Among the extraterrestrial objects, native rhenium was found in Ni-iron and silicates from the Allende meteorite ."
The image on the right contains small particles of native rhodium-bearing ferroplatinum. This sample was obtained from the lunar regolith "by the Luna-16 automatic station".
"Terrestrial iron-free rhodium-bearing platinum with the composition of Pt0.68Rh0.32 in association with platinum-bearing rhodium Rh0.57Pt0.43 [...] was originally discovered in heavy fractions from basic rocks (norite, gabbro, and anorthosite) in the upper zone of the layered Stillwater intrusion (Montana, United States) ."
The piece of native ruthenium in the image on the right contains some iridium. It is from Verkhneivinsk, Neiva river, Sverdlovskaya Oblast', Middle Urals, Urals Region, Russia.
- Precious metals have variable value so may only be used as an interim investment.
- Willard Lincoln Roberts, George Robert Rapp, Jr., and Julius Weber (1974). Encyclopedia of Minerals. 450 West 33rd Street, New York, New York 10001 USA: Van Nostrand Reinhold Company. pp. 121–2. ISBN 0-442-26820-3.
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- A. F. Grachev, S. E. Borisovsky, and A. V. Grigor’eva (October 2008). "The first find of native rhenium in the transitional clay layer at the Cretaceous/Paleogene boundary in the Gams Section (eastern Alps, Austria)". Doklady Earth Sciences 422 (1): 1065-7. doi:10.1134/S1028334X08070131. http://link.springer.com/article/10.1134/S1028334X08070131. Retrieved 2015-11-04.
- T. A. Gornostaeva, P. M. Kartashov, A. V. Mokhov, and O. A. Bogatikov (2012). "Native Rhodium-Bearing Ferroplatinum in a Lunar Regolith Sample from the Mare Fecunditatis". Doklady Earth Sciences 444 (2): 770-2. doi:10.1134/S1028334X12060220. http://link.springer.com/article/10.1134/S1028334X12060220#/page-1. Retrieved 2015-11-04.