Quartz

Quartz Crystal found at Hansen Creek (west of Snoqualmie Pass)

WHAT IS IT?

  • Silicon Dioxide (Si02) - Constitutes 12% of the earth’s crust (2nd most abundant mineral after feldspar, which constitutes up to 60%)

HISTORY

  • The name is derived from the German word "Quarz'. The Middle High German name is “twarc", which has roots to the Slavic word “Tvrdy", meaning "hard"

  • The Chinese used smokey quartz to make sunglass lenses in the 12th century

  • Used by ancient Mediterranean cultures (Minoan, Roman, Greek) for impression seals (intaglios), jewelry and tools (knives)

TYPES OF QUARTZ

  • There are many varieties (some are semi-precious gemstones). This is an incomplete list:

    • Agate- multi-colored, banded, translucent or semi-translucent chalcedony

    • Amethyst - clear purple colored quartz containing trace amounts of iron with transition metals

    • Ametrine - a combination of amethyst & citrine

    • Aventurine - a green translucent chalcedony that shimmers due to Inclusions (usually containing mica)

    • Carnelian - a translucent, reddish-orange chalcedony

    • Chalcedony - a white or light colored material consisting of a mixture of cryptocrystalline quartz (microscopic crystals) & moganite

    • Citrine - quartz that contains iron pigmentation resulting in a yellow to brown color. It is indistinguishable from yellow topaz except for hardness (topaz is harder).  It is often made by heat-treating amethyst or smokey quartz

    • Chrysoprase- a green variety of chalcedony that is colored by nickel oxide

    • Dumortierite quartz — quartz that contains dumortierite crystals (fibrous aluminum-boro silicate)

    • Heliotrope or Bloodstone — a green variety of chalcedony containing red inclusions of iron oxide

    • Jasper - a cryptocrystalline opaque variety that typically has a red or brown color

    • Milky quartz - an opaque white appearance that is caused by minute inclusions of liquid, gas, or a combination of the two. It is the most common variety of quartz and is found almost anywhere.

    • Mtorlite or Chrome Chalcedony — a green variety of chalcedony that gets its color from chrome

    • Onyx is a form of agate that has parallel evenly spaced bands of black and white

    • Prasiolite (aka green quartz or vermarine) - a rare green form of quartz once mined in Brazil & Poland, now only synthetic

    • Rock crystal or clear quartz - colorless & transparent (clear)

    • Rose quartz - a dull pink to rose colored variety that contains iron, manganese, and/or titanium. A rarer variety contains phosphorus and aluminum. Some exhibits diasterism (displays a luminous star pattern when illuminated from back)

    • Sardonyx - similar to onyx but has brown, orange, red, and white banding

    • Smoky quartz - varies from being translucent gray to an almost opaque grey-brown due to natural irradiation. There are a number of varieties (e.g._ Moran, Cairngorm). Contains uranium trioxide

    • Tiger's eye - a fiberous variety that exhibits chatoyancy and is usually orange to red-brown in color

  • Quartz-like or quartz derived silica minerals:

    • Coesite — danse polymorph of quartz found at meteorite impact Sites

    • Cristobalite — high-temp polymorph of quartz found in volcanic rock

    • Lechatelierite — an amorphous silica glass formed by lightning strikes

    • Moganite — a monoclinic polymorph of quartz discovered in 1984 (has same chemical composition, but a different structure). Typically constitutes from less than 5% to more than 20% of the mass of a typical chalcedony

    • Stishovite — a very dense polymorph of quartz found at meteorite impact sites (denser than coesite)

    • Tridymite — another high-temp polymorph of quartz found in volcanic rock

WHERE IS IT FOUND?

  • Quartz is found worldwide (e.g. most beach sand contains it; granite contains it). Agate, jasper, and milky quartz are common.

  • Amethyst— Brazil, Mexico, Uruguay, Russia, France, Namibia and Morocco (best sources)

  • Aventurine —Austria, Brazil, Chile, India, Spain, Russia, Tanzania

  • Carnelian — Brazil, India, Uruguay

  • Citrine — Brazil

  • Chrysoprase — Australia, India, Russia, USA

  • Heliotrope — India primarily. Also, Australia, Bran, China, Scotland (Isle of Rum), USA

  • Onyx — Brazil, Madagascar, Uruguay

  • Parsiolite — no current natural sources. Made by heat-treating amethyst and citrine (primarily from Brazil)

  • Rose quartz - Brazil, Madagascar, India, United States, Japan, Africa, Germany and Switzerland

  • Sardonyx — Brazil, Czech Republic, Germany, Sri Lanka, Uruguay, USA (Great Lakes, Oregon)

  • Smoky quartz— Australia, Brazil, Canada, China, England, Ghana, Hungary, India, Madagascar, Mozambique, Scotland, Slovakia, Sweden, Switzerland, and the United States (in numerous states, esp. Arkansas; also Crystal Park near Dillon, MT)

WHAT IS IT USED FOR?

  • Jewelry, carvings, collector specimens, heat lamps, prisms, lenses, paints, refractories, abrasives, precision instruments

  • Has piezoelectic properties - useful for electronic oscillator crystals (digital watches, computers & radios) & sensors