Geological Properties Of Quartz
Geological Properties Of Quartz, Quartz has been known and appreciated since pre-historic times. The most ancient name known is recorded by Theophrastus in about 300-325 BCE, κρύσταλλος or kristallos. The varietal names, rock crystal and berg crystal, preserve the ancient usage. The root words κρύοσ signifying ice cold and στέλλειυ to contract (or solidify) suggest the ancient belief that kristallos was permanently solidified ice.
The earliest printed use of “querz” was anonymously published in 1505, but attributed to a physician in Freiberg, Germany, Ulrich Rülein von Kalbe (a.k.a. Rülein von Calw, 1527). Agricola used the spelling “quarzum” (Agricola 1530) as well as “querze”, but Agricola also referred to “crystallum”, “silicum”, “silex”, and silice”. Tomkeieff (1941) suggested an etymology for quartz: “The Saxon miners called large veins – Gänge, and the small cross veins or stringers – Querklüfte. The name ore (Erz, Ertz) was applied to the metallic minerals, the gangue or to the vein material as a whole. In the Erzgebirge, silver ore is frequently found in small cross veins composed of silica. It may be that this ore was called by the Saxon miners ‘Querkluftertz’ or the cross-vein-ore. Such a clumsy word as ‘Querkluftertz’ could easily be condensed to ‘Querertz’ and then to ‘Quertz’, and eventually become ‘Quarz’ in German, ‘quarzum’ in Latin and ‘quartz’ in English.” Tomkeieff (1941, q.v.) noted that “quarz”, in its various spellings, was not used by other noted contemporary authors. “Quarz” was used in later literature referring to the Saxony mining district, but seldom elsewhere.
Geological Properties Of Quartz
Gradually, there were more references to quartz: E. Brown in 1685 and Johan Gottschalk Wallerius in 1747. In 1669, Nicolaus Steno (Niels Steensen) obliquely formulated the concept of the constancy of interfacial angles in the caption of an illustration of quartz crystals. He referred to them as “cristallus” and “crystallus montium”.
Tomkeieff (1941) also noted that Erasmus Bartholinus (1669) used the various spellings for “crystal” to signify other species than quartz and that crystal could refer to other “angulata corpora” (bodies with angles): “In any case in the second half of the XVIIIth century quartz became established as a name of a particular mineral and the name crystal became a generic term synonymous with the old term ‘corpus angulatum’.”
Description
Quartz is one of the most common minerals in the Earth’s crust. As a mineral name, quartz refers to a specific chemical compound (silicon dioxide, or silica, SiO2), having a specific crystalline form (hexagonal). It is found is all forms of rock: igneous, metamorphic and sedimentary. Quartz is physically and chemically resistant to weathering. When quartz-bearing rocks become weathered and eroded, the grains of resistant quartz are concentrated in the soil, in rivers, and on beaches. The white sands typically found in river beds and on beaches are usually composed mainly of quartz, with some white or pink feldspar as well.
Geological Properties Of Quartz
Morphology
Quartz is found as individual crystals and as crystal aggregates. Well crystallized quartz crystals are typically six-sided prisms with steep pyramidal terminations. They can be stubby (“short prismatic”) or elongated and even needle-like. In most environments quartz crystals are attached to the host rock and only have one tip, but double-terminated crystals are also found.
As a rock-forming mineral, quartz commonly occurs as sub-millimeter to centimeter-sized anhedral grains, well-formed crystals are uncommon. Secondary vein-fillings of quartz are typically massive.
Quartz belongs to the trigonal-trapezohedral crystal class 32. Of the seven basic crystallographic forms of this crystal class, the hexagonal prism and trigonal rhombohedra are very common and determine the overall shape of the crystals. The trigonal bipyramids and trigonal trapezohedra are frequently found, but typically only as relatively small faces. The trigonal prisms, the basal pinacoid and in particular ditrigonal prisms are very rare (Frondel, 1962).
Quartz crystals show about 100 different crystallographic forms in nature (Frondel, 1962; Rykart, 1995). It is convenient and common practice to designate them with Latin and Greek letter symbols instead of Miller-Bravais indices. The following figure illustrates the relation of the common forms (sorted by abundance) to the faces found on quartz crystals. The most common combination of crystallographic forms in quartz crystals is r+m+z.
Relation to Mining
Quartz crystal is found in many countries and many geologic environments. Major producers of natural quartz crystals are the United States (particularly Arkansas) and Brazil. Natural quartz is rarely used as found in nature (especially in electrical applications), except as a gemstone. Natural quartz crystals have too many chemical impurities and physical flaws. As a result, a commercial process of manufacturing pure, flawless, electronics-grade quartz was developed. “Cultured quartz,” that is, quartz crystals grown very carefully in highly controlled laboratory conditions, is the quartz that is used in industry. About 200 metric tons of cultured quartz is produced each year. In the production of cultured quartz crystals, a “seed crystal” is needed. A seed crystal is a small piece of carefully selected, non-electronics-grade quartz. The manufactured crystal grows on this seed crystal.
Uses
Quartz crystal is one of several minerals which are piezoelectric, meaning that when pressure is applied to quartz, a positive electrical charge is created at one end of the crystal and a negative electrical charge is created at the other. These properties make quartz valuable in electronics applications. Electronics-grade manufactured quartz is used in a large number of circuits for consumer electronics products such as computers, cell phones, televisions, radios, electronic games, etc. It is also used to make frequency control devices and electronic filters that remove defined electromagnetic frequencies.
Physical Properties Of Quartz
Type: Mineral
Mineral Classification: Silicate
Chemical Formula: SiO2
Streak: White
Mohs Hardness: 7
Crystal System: trigonal
Color: Pure quartz is clear. Color variance due to impurities: purple (amethyst), white (milky quartz), black (smoky quartz), pink (rose quartz) and yellow or orange (citrine).
Luster: vitreous, waxy, dull
Fracture: conchoidal
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