[link|http://216.239.39.100/search?q=cache:liV3X-9VnBQC:minerals.usgs.gov/minerals/pubs/commodity/mica/440499.pdf+mica+strategic+insulation&hl=en|USGS page (HTML view)]:
The value of mica is in its unique physical properties. The crystalline structure of mica forms mineral layers that can be split or delaminated into thin sheets. These sheets are flexible, elastic, platy, transparent to opaque, resilient, reflective, refractive, dielectric, chemically inert, insulating, lightweight, and hydrophilic. Mica also is stable when exposed to electricity, light, moisture, and extreme temperatures. Based on its greater abundance and superior electrical properties, muscovite is the principal mica used by industry. Phlogopite remains stable at higher temperatures and is used in applications where a combination of high-heat stability and electrical properties is required. Muscovite and phlogopite are used in sheet and ground forms.
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Essentially all sheet mica used in the United States was imported, primarily from India.
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Sheet Mica.- Sheet mica is used principally in the electronic and electrical industries. Its usefulness in these applications is derived from its unique electrical and thermal insulating properties and its mechanical properties, which allow it to be cut, punched, stamped, and machined to close tolerances.
The largest use of block mica is as an electrical insulator in electronic equipment. High-quality block mica is processed to line the gauge glasses of high-pressure steam boilers because of its transparency, flexibility, and resistance to heat and chemical attack. Other uses include diaphragms for oxygen-breathing equipment, marker dials for navigation compasses, optical filters, retardation plates in helium-neon lasers, pyrometers, thermal regulators, and stove and kerosene heater windows. Specialized applications for sheet mica are found in aerospace components in ground- and air-launched missile systems, optical instrumentation, laser devices, medical electronics for radiation treatment, and radar systems.
If India cut off sheet mica exports to the US, and the stockpile ran out, the US military would have difficulty. Similarly, if Saudi Arabia cut off oil exports to the US, and the stockpile ran out, the US military would have difficulty.
Similar pages exist for the other materials on BP's list.
Cheers,
Scott.