HISTORY, NAME, LOCALITIES: Muscovite has been known since antiquity when it was called “white mica” and used in powdered form to whiten paints. In 1850, it was assigned its name, which stems from the Russian principality of Muscovia (Moscow), where thin sheets called “isinglass” were used as a substitute for glass in windows and ovens. Notable collecting localities are found in Namibia, Russia, Brazil, Pakistan, Malawi, Austria, Madagascar, and the United States (Maine, Vermont, South Dakota, Colorado, New Mexico, California, Virginia).
MINERALOGY, PROPERTIES, OCCURRENCE: Muscovite [basic potassium aluminum silicate, KAl2ALSi3O10(OH)2], pronounced MUSS-coh-vite, crystallizes in the monoclinic system as thin, tough, elastic, sheet-like crystals aligned parallel to its perfect, one directional cleavage. Muscovite is a phyllosilicate mineral with a Mohs hardness of 2.0-2.5, vitreous-to-pearly luster, specific gravity of 2.7-3.0, and tendency to form aggregates of well-developed crystals called “mica books.” Muscovite cleaves easily into thin, semi-transparent, silvery-white sheets. As an abundant rock-forming mineral, muscovite is an essential component of many igneous, metamorphic, and sedimentary rocks and achieves its best crystal development in granite pegmatites.
METAPHYSICAL PROPERTIES; LORE, USES: Metaphysical practitioners believe that muscovite aids problem solving, stimulates quickwittedness, and alleviates anger, stress, and self-doubt. Because of its low coefficients of friction and thermal expansion, inertness, and excellent heat- and electrical-insulating properties, muscovite has many uses in industry and is mined extensively.
COLLECTING INFORMATION: Muscovite is collected for its unusual crystal forms, usually as composite specimens in association with such pegmatite minerals as beryl, quartz, and microcline.
QUARTZ (var. ROCK CRYSTAL)
HISTORY, NAME, LOCALITIES: Rock crystal, which is common and occurs worldwide, has been collected since prehistory. Notable collecting localities are found in India, Brazil, Germany, Peru, Bolivia, Namibia, Russia, and the United States (Arkansas, Colorado, Maine, Connecticut, Virginia).
MINERALOGY, PROPERTIES, OCCURRENCE: Rock crystal is the transparent, colorless variety of macrocrystalline quartz [silicon dioxide, SiO2). The word “quartz” is believed to have originated with the Slavic kwardy, meaning “hard,” in allusion to its substantial hardness. It crystallizes in the hexagonal system and occurs mainly in hydrothermal veins, granite pegmatites, and as geode linings as short-to-long, horizontally striated, hexagonal, prismatic crystals with pyramidal terminations and distinctive, water-clear transparency. It has a Mohs hardness of 7.0, a conchoidal fracture, vitreous luster, and specific gravity of 2.65.
METAPHYSICAL PROPERTIES, LORE, USES: Rock crystal has since antiquity been one of the most widely collected of all minerals. It has served as a gemstone and ornamental stone in many cultures. Until quartz was synthesized in the 1960s, rock crystal was vital to electronic frequency controls, filters, and timing devices. Modern metaphysical practitioners call rock crystal the “universal crystal” because of its numerous abilities to sharpen insight, enhance spiritual development, improve concentration, refine focus, and energize the mind.
COLLECTORS’ INFORMATION: Rock crystal is widely collected for its brilliant transparency, superb hexagonal crystal development, and frequent occurrence on large plates and in geodes to make interesting display pieces.