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There is more information available on this subject at Platinum on the English Wikipedia.

Platinum (pronounced /ˈplætɪnəm/) is a chemical element with the atomic symbol Pt and an atomic number of 78. It is in group 10 of the Periodic Table of Elements. A heavy, malleable, ductile, precious, gray-white transition metal, platinum is resistant to corrosion and occurs in some nickel and copper ores along with some native deposits. Platinum is used in jewelry, laboratory equipment, electrical contacts, dentistry, and automobile emissions control devices. Platinum bullion has the ISO currency code of XPT.

The Covenant use platinum in their ships, notably their holographic projectors.[1]