PRECIOUS METALS
GOLD   PLATINUM   SILVER
created by
Jeff McPherson

This is a student created web page for a Mineralogy class at Emporia State University. This page will cover the properties of the precious metals: gold, platinum, and silver. Information given will be chemical name, class, group, geographic occurrence, and uses. I have also included physical characteristics such as, color, luster, transparancy, crystal system, crystal habits, cleavage, fracture, streak, hardness, specific gravity, and associated minerals. I hope this page is helpful to you in learning more about these natural wonders.

Gold


Native Gold
Au
Image taken from: http://mineral.galleries.com/minerals/elements/gold/gold.htm

NAME ORIGIN: Thought to be from the Anglo-Saxon word, geld, meaning yellow.
CLASS:Native Elements.
GROUP: Gold.
CRYSTAL SYSTEM: Isometric; 4/m Bar3 2/m. Crystals are most commonly octahedral in shape but can be found to have faces of the dodecahedron, cube, and trapazoid.
CRYSTAL HABITS: Include massive nuggets, dissememinated grains, wires, dendritic and arborescent crystal clusters.
SPECIFIC GRAVITY: 19.3+ (extremely heavy, even for a metallic minerals.)
HARDNESS: 2.5-3
COLOR: Various shades of yellow, depending on purity. It becomes paler with the increase of included silver.
LUSTER: Metallic.
TRANSPARENCY: Opaque.
CLEAVAGE: None.
FRACTURE: Hackly.
STREAK: Golden yellow.
OTHER CHARACTERISTICS: It is ductile, malleable and sectile, which means it can be stretched into extremely thin wires, hammered into thin sheets, and cut into shavings.
BEST INDICATORS OF GOLD FOR FIELD IDENTIFICATION: Color, density, hardness, and tenacity, such as sectility, malleability and ductility.
MOST NOTABLE OCCURENCES: California and South Dakota, USA; Siberia, Russia; South Africa; Canada and many other areas around the world.
ASSOCIATED MINERALS: Quartz, nagyagite, calaverite, sylvanite, krennerite and pyrite.
KARAT: A measurment of fineness or purity equal to 1/24 pure gold in an alloy. 24 Karat gold, or pure gold, is extremely soft, so it must be alloyed, or combined, with other minerals to increase its strength and durability.

Measurement of the Purity of Gold
Karatage Gold Content Fineness
24K 100% 999
18K 75% 750
14K 58% 585
12K 50% 500
10K 41% 416

USES FOR GOLD: Because it is very malleable and durable, it is perfect for jewelry and ornamentation. It is also made into small bars and medallions for investment purposes. Some think that gold may have been the first metal used by humans, at this time it was valued for ornaments and it was said to possess magical powers. Other uses for gold include scientific instruments, electroplating, gold leaf and dental applications. Gold can also be stretched into extrememly thin wires which are very useful in computers.

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Platinum


Platinum
Pt
Image taken from: http://mineral.galleries.com/minerals/elements/platinum/platinum.htm

NAME ORIGIN: Derived from the spanish word plata, "silver," which describes the bright color of the mineral.
CLASS: Native Elements.
GROUP: Platinum.
CRYSTAL SYSTEM: Isometric; 4/m Bar 3 2/m.
CRYSTAL HABITS: Nuggets, grains or flakes, is also seen very rarely in cubic forms.
SPECIFIC GRAVITY: 14-19+. Its pure form is 21.5, (extremely heavy, even for metallic minerals.)
HARDNESS: 4-4.5.
COLOR: White-gray to silver-gray.
LUSTER: Metallic.
TRANSPARENCY: Opaque.
CLEAVAGE: None.
FRACTURE: Hackly.
STREAK: Steel-gray.
OTHER CHARACTERISTICS: Does not tarnish, can have a weak magnetism, is ductile, malleable and sectile, which means it can be pounded into different shapes, it can be stretched into thin wires, and it can be cut into slices.
BEST INDICATORS OF PLATINUM FOR FIELD INDENTIFICATION: Color, density, weak magnetism, hardness, associations and ductility.
MOST NOTABLE OCCURENCES: Transvaal, South Africa; Ural mountains, Russia; Columbia and Alaska, USA.
ASSOCIATED MINERALS: Chromite, olivine, enstatite, pyroxene, magnetite and gold.
USES FOR PLATINUM: The two most common uses of platinum are as a catalytic converter for the automobile industry and as jewelry. Platinum's high melting point of 1755º C make it perfect for this. Platinums ability to withstand high temperatures also makes it perfect for jet fuel nozzles. Other uses include electrical equipment, dentistry, surgical instruments, and jewelry.

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Silver


Silver
Ag
Image taken from: http://mineral.galleries.com/minerals/elements/silver/silver.htm

NAME ORIGIN: Derived from the Old Eglish word, "seolfor."
CLASS: Elements.
GROUP: Gold.
CRYSTAL SYSTEM: Isometric; 4/m Bar 3 2/m.
CRYSTAL HABITS: Massive and disseminated grains, wires and plates are the most common. It is very rare to have whole individual crystals, but when they are present they are cubes, dodecahedrons and octahedrons.
SPECIFIC GRAVITY: Varies according to purity 10-12, (well above average for metallic minerals.)
HARDNESS: 2.5-3.
COLOR: Silver-white. Specimens can tarnish to black.
LUSTER: Metallic.
TRANSPARENCY: Opaque.
CLEAVAGE: None.
FRACTURE: Hackly.
STREAK: Silver-white.
OTHER CHARACTERISTICS: Ductile, malleable and sectile, which means it can be pounded into different shapes, it can be stretched into extremely thin wires and it can be cut into slices.
BEST INDICATORS OF SILVER FOR FIELD IDENTIFICATION: Color, ductility, crystal habit and the fact that it will tarnish.
MOST NOTABLE OCCURENCES: Michigan and Arizona, USA; Cobalt, Ontario; Chile; and Germany.
ASSOCIATED MINERALS: Acanthite, prousite, cobaltite, copper, zeolites and quartz.
USES: Its main use is in photographic film, it is also used in plating, brazing alloys, tableware, electronic equipment and of course jewelry.

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This page was created December 9, 1999. Links updated 29 February, 2004. Questions? Email mcphersj@esuvm.emporia.edu.

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