Name/Title
Quartzite / SillimaniteEntry/Object ID
2010.1.55Description
Chemical Composition: SiO2
Crystal System: Hexagonal System
Description: Common Name: Quartzite / Sillimanite
Chemistry: Si O2 / Al2 Si O5
Class: Silicates
Location: Unknown
Description: Large, thin slab with polished face. Beige and tan in majority of specimen with spots of light-blue crystals and some light-tan streaking throughout.
PHYSICAL CHARACTERISTICS:
Color is as variable as the spectrum, but clear quartz is by far the most common color followed by white or cloudy (milky quartz). Purple (Amethyst), pink (Rose Quartz), gray or brown to black (Smoky Quartz) are also common. Cryptocrystalline varieties can be multicolored.
Luster is glassy to vitreous as crystals, while cryptocrystalline forms are usually waxy to dull but can be vitreous.
Transparency: Crystals are transparent to translucent, cryptocrystalline forms can be translucent or opaque.
Crystal System is trigonal; 3 2.
Crystal Habits are again widely variable but the most common habit is hexagonal prisms terminated with a six sided pyramid (actually two rhombohedrons). Three of the six sides of the pyramid may dominate causing the pyramid to be or look three sided. Left and right handed crystals are possible and identifiable only if minor trigonal pyramidal faces are present. Druse forms (crystal lined rock with just the pyramids showing) are also common. Massive forms can be just about any type but common forms include botryoidal, globular, stalactitic, crusts of agate such as lining the interior of a geode and many many more.
Cleavage is very weak in three directions (rhombohedral).
Fracture is conchoidal.
Hardness is 7, less in cryptocrystalline forms.
Specific Gravity is 2.65 or less if cryptocrystalline. (average)
Streak is white.
Other Characteristics: Striations on prism faces run perpendicular to C axis, piezoelectric (see tourmaline) and index of refraction is 1.55.
Associated Minerals are numerous and varied but here are some of the more classic associations of quartz (although any list of associated minerals of quartz is only a partial list): amazonite a variety of microcline, tourmalines especially elbaite, wolframite, pyrite, rutile, zeolites, fluorite, calcite, gold, muscovite, topaz, beryl, hematite and spodumene.
Best Field Indicators are first the fact that it is very common (always assume transparent clear crystals may be quartz), crystal habit, hardness, striations, good conchoidal fracture and lack of good cleavage.
Fracture: Conchoidal
Hardness: 7 Quartz
Luster: Waxy
Occurrence: Background:
Quartzite is a nonfoliated metamorphic rock that formed by the metamorphism of pure quartz sandstone. The intense heat and pressure of metamorphism causes the quartz grains to compact and become tightly intergrown with each other, resulting in very hard and dense quartzite. Quartzite is usually white or gray, but can be other light colors depending on the impurities in the parent sandstone. It has a glassy luster, as would be expected considering the quartz in sandstone has a vitreous or glassy luster. When quartzite weathers it can have a granular appearance, but freshly broken surfaces break in even surfaces because the break goes through the intergrown quartz grains. (By comparison, sandstone breaks around the quartz grains and therefore shows a granular appearance on a freshly broken surface.) They can form anywhere heat and pressure change pre-existing sandstone deposits, so quartzite is found both in geologic settings of regional metamorphism (where metamorphism occurs more from pressure than heat) and contact metamorphism (where metamorphism occurs more from heat than pressure). However, quartzite most typically forms during mountain-building events where continents collide with each other. Because it is so dense and tough, quartzite is extremely resistant to weathering and erosion.
Sources:
Geologically speaking quartzite occurs in regions of regional, high-pressure metamorphism. In the United States quartzite quarries are found in Idaho, New York, Wisconsin, Pennsylvania, Minnesota, Montana, Arizona and South Dakota. Because it is so dense and resistant to both physical and chemical weathering, it is poor bedrock on which to form soil. As a result, typically-quarried quartzite is very near the surface. Because it is so hard and dense, quartzite has not been quarried as extensively as other softer dimension stone (such as limestone, sandstone and granite), although construction industry experts estimate that present demand exceeds annual production. A total of 1.3 billion tons of crushed rock is produced in the United States annually. Of this, less than 6% is quartzite. In fact, sandstone, marble, scoria, volcanic cinder and miscellaneous stone - all together - account for less than 6% of the total crushed stone production in the U.S.
Uses:
Quartzite is becoming more popular as a dimension stone in the construction industry. The use of quartzite as decorative stone in building construction is growing annually. As noted above, quartzite breaks into flat surfaces. Consequently, quartzite slabs are used to cover walls, as roofing tiles, as flooring, and stair steps to name just a few applications.
Quartzite is also used, to a small degree, as crushed stone. The vast majority of crushed stone - about 85% - is used in road construction and repair. In the United States, most crushed stone produced is limestone, granite, and trap rock. Limestone represents 70% of all the crushed rock produced.
Rock Type: Sedimentary
Specific Gravity: 2.58-2.64
Streak: WhiteCollection
RAGM Mineral CollectionAcquisition
Accession
2009.62Source or Donor
Museum Collection of MineralsAcquisition Method
DonationDimensions
Width
9-1/4 inDepth
1-1/2 inLength
14 inLocation
Location
Shelf
CenterCabinet
Case# 133Building
Frieda Smith HallCategory
Permanent