Name/Title
Muscovite / AlbiteEntry/Object ID
2009.62.145Description
Description: Common Name: Muscovite / Albite
Chemistry: KAl2(AlSi3O10)(F, OH)2, Potassium aluminum silicate hydroxide fluoride / NaAlSi3 O8, Sodium aluminum silicate.
Class: Silicates
Location: Minas Gerais, Brazil
Description: Highly dense, somewhat linear, segmented, worm-like dull white to tan crystals with star shaped layered light brown crystals imbedded within it.
PHYSICAL CHARACTERISTICS OF MUSCOVITE:
Color is white, silver, yellow, green and brown.
Luster is vitreous to pearly.
Transparency crystals are transparent to translucent.
Crystal System is monoclinic; 2/m
Crystal Habits include tabular crystals with a prominant pinacoid termination. Muscovites four prism faces form diamond shaped "books" and if modified by another pinacoid they form pseudo-hexagonal crystal "books". The sides of the crystal often tend to tapper. Also as lamellar rock forming masses and small flakes in detrital matterial. Twinned crystals can form flat five pointed stars.
Cleavage is perfect in one direction producing thin sheets or flakes.
Fracture is not readily observed due to cleavage but is uneven.
Hardness is 2 - 2.5.
Specific Gravity is approximately 2.8 (average)
Streak is white.
Associated Minerals are quartz, feldspars, beryl and tourmalines.
Other Characteristics: cleavage sheets are flexible and elastic, meaning they can be bent and will flex back to original shape.
Best Field Indicators are crystal habit, cleavage, elastic sheets, color and associations.
PHYSICAL CHARACTERISTICS OF ALBITE:
Color is usually white (Albite is derived from the same root word as albino) or colorless but can be shades of blue, yellow, orange and brown.
Luster is vitreous to dull if weathered..
Transparency crystals are translucent to opaque and only sometimes transparent.
Crystal System is triclinic; bar 1
Crystal Habits include blocky, tabular and platy crystals. The typical crystal has a nearly rectangular or square cross-section with slightly slanted dome and pinacoid terminations. A variety called Cleavelandite forms very thin platy crystals that can grow rather large (15+ cm across) but can maintain an even thickness of only a few millimeters. Twinning is almost universal in albite. Crystals can be twinned according to the Albite, Carlsbad, Manebach and Baveno laws. Albite is a common constituent of granitic and syenite rocks. Can also be massive.
Cleavage is perfect in one and good in another direction forming nearly right angled prisms.
Fracture is conchoidal.
Hardness is 6 - 6.5.
Specific Gravity is approximately 2.61 (average)
Streak is white.
Associated Minerals are quartz, tourmaline and muscovite.
Other Characteristics: index of refraction is 1.53. Lamellar twinning may cause a grooved effect on cystal surfaces that appear as striations. Some albite may show an opalescence due to twinning and is referred to as moonstone.
Best Field Indicators are occurence, crystal habit, twinning, striations, density and index of refraction.
Occurrence: Notable Occurrences include India, Pakistan, Brazil and many USA locallities.
Variety: Muscovite is a common rock forming mineral and is found in igneous, metamorphic and detrital sedimentary rocks.Collection
RAGM Mineral CollectionAcquisition
Accession
2009.62Source or Donor
Museum Collection of MineralsAcquisition Method
DonationLocation
Location
Shelf
CS-E-1Room
Curation StorageBuilding
Crater Rock MuseumCategory
StorageMoved By
Jillian Mather KettleyDate
February 23, 2024
