Stone Information - Quartz PDF

***Quartz & Chalcedony***** LARGEST CONSUMERS : Rock Crystal: China & USA MOHS SCALE: 7 VARIETY/SPECIES/GROUP: Quartz (larger crystal structure) Chalcedony (Quartz species w/smaller crystal structure) COLOR/HUE RANGE/VALUE: Amethyst: hues range is strongly saturated violetish purple to reddish purpl...

***Quartz & Chalcedony***** LARGEST CONSUMERS : Rock Crystal: China & USA MOHS SCALE: 7 VARIETY/SPECIES/GROUP: Quartz (larger crystal structure) Chalcedony (Quartz species w/smaller crystal structure) COLOR/HUE RANGE/VALUE: Amethyst: hues range is strongly saturated violetish purple to reddish purple in fine quality, with saturation of medium-dark to dark reddish purple or purple, to weak grayish violet hue in commercial quality, tone is very light to very dark, medium, brownish or bronze-colored tints or color zoning effect the price Citrine: transparent, yellow to brownish orange variety of quartz, high quality is saturated yellow to reddish orange color, free of brownish tints, most popular is a deep brownish or reddish orange. - intense greenish yellow to yellowish green quartz has been marketed as "Lemon Quartz", Lemon quartz is smoky quartz that is irradiated and then heated. Ametrine: transparent bicolor variety of quartz containing both amethyst and citrine, medium-dark to moderately strong orange and vivid to strong purple or violetish purple Smoky Quartz: (also know as "Cairngorm") light yellowish brown or orange-brown to a dark brown that’s almost black,Very dark brown smoky quartz is called morion, best-quality is a deep reddish brown and also displays orange-red pleochroic flashes Rose Quartz: very light pink (almost white) to medium-dark pink, finest is normally highly transparent Rock Crystal: colorless, transparent quartz -"tourmalinated quartz" has dark-hued tourmaline inclusions -"rutilated quartz" or Venus hair stone have Hair-thin reddish or golden rutile crystals Cat's Eye Quartz: semitransparent to trans­lucent brownish yellow, brownish green, or greenish yellow Tiger's Eye Quartz: semitranslucent to opaque gem has a pattern of lustrous yellow and brown bands that reverse color, "zebra tiger’s-eye"variegated grayish blue and brown variety, "hawk’s-eye or falcon’s-eye" the quartz is a grayish blue color, Both tiger’s-eye and hawk’s-eye are microcrystalline aggregatess Quartzite: coarse aggregate of tightly packed quartz grains, one type "Aventurine quartz" translucent to opaque with small inclusions of mica or other minerals (green mica is common) CHEMICAL COMPOSTION: All Quartz varieties have a base of silicon and oxygen Amethyst- trace element is iron, Citrine's - trace elements is iron, Smoky Quartz- natural radiation involve aluminum impurities FORMING SOURCE: pegmatite and volcanic and sedimentary rocks. CRYSTAL STRUCTURE: all fall under the trigonal crystal system (Quartz & Chalcedony) with different sizes -Large single or twinned crystals -Microcrystalline aggregates of small, but not microscopic, crystals -Cryptocrystalline aggregates of tiny microscopic crystals (all Chalcedony) POSSIBLE PHENMENOM: Chatoyant, Aventurscence, Rose Quartz: numerous small inclusions can create asterism Rock crystal & Smoky quartz can have "phantom effects" is a v-shaped color band visible with the unaided eye CLARIETY CHARACTERISTIC: Amethyst: Color zoning and inclusions, Citrine: color zoning and inclusions, Rose Quartz: tends to internal fractures giving a cloudy translucence Rock Crystal: eye inclusions, "Sagenitic quartz" or sagenite has eye-visible needle-like mineral inclusions typically named after the type of inclusions it has(rutile is common) COMMON TREATMENTS: Amethyst: Heat treatment is most common to lighten dark stones ( it can also be heated to turn yellow) Heat treatment can also produce green quartz also called "prasiolite" Citrine: natural citrine is rare, most on the market is the result of heat treatment Ametrine: heat treatment or of a combination of heat treatment and irradiation, most likely coming from colorzoned amethyst. Smoky Quartz: heat treating can lighten very dark smoky quartz, also heat treated, smoky quartz changes to a greenish yellow resembling citrine, separately irradiating rock crystal quartz in the lab Rose Quartz: treated with irradiation to intensify its color Rock Crystal: quench-crackled—heated treated to display rainbow iridescence, quench crackle dye can mimic ruby or emerald, metallic coating is done to create variety of colors( gold coating is popular giving the effect of iridescent blue or blue-green color know as “aqua aura,” Tiger's Eye Quartz: heat treated to produce a reddish brown color, bleached to produce a lighter brown and dyed to bright blues, greens, or reds. Quartzite: often dyed to resemble jade COMMON CUTS: Amethyst: variety of fancy cuts as well as calibrated sizes (most popular being oval 6x4 & 7x5), non eye clean gems are cut into cabochons Citrine: comes in most fancy cuts and unusual cuts & carvings Ametrine: often cut into emerald cut with a focus on half & half distburtion , mixed cuts or brilliant cuts, free form cuts & fantasy cuts are also popular Rose Quartz: tends to grow in large crystals, well shaped specimens are prized high, typically cut into beads & cabochons Rocky Crystal: rough crystals vary in size from minute to enormous, faceted, beads, and large scale carvings Tiger's Eye: tablets, beads, domed cabochons, (tiger’s-eye nor hawk’s-eye requires a curved surface to display chatoyancy) Quartzite: small ornamental carvings TRADES NAMES: Amethyst- "Maraba" (from Para State in Brazil), Smokey Quartz -"Cairngorm" after the Cairngorm Mountains of Scotland where it is mined COUNTRIES OF ORIGIN: Amethyst: Africa, South America /Brazil & Zambia Zambia:(which are sometimes too dark, smaller with deep color, started to be popular begin in 1980's), production comes from Kariba mine in southern part of Zambia’s Kalomo District 87% owed by the Zambia government Brazil: make up 50% of the calibrated commercial amethyst, top states for production are Para in the north, and Rio Grande do Su, Alto Bonito Uruguay & Argentina typically have strong color zoning, The Four Peaks Mine in Arizona reopened in 1998 and and provides fine amethyst, Other sources of amethyst include Canada, India, Madagascar, Mexico, Myanmar, Namibia, Sri Lanka, Tanzania, and Morocco, historically Russia was a source during the 19th century COUNTRIES OF ORIGIN continued: Citrine: natural citrine are Bolivia, Spain, Madagascar, Mexico, and Uruguay, heat treated amethyst made into citrine is mostly mined in Brazil Ametrine: one source of natural ametrine: a deposit in eastern Bolivia at the Anahí mine Smoky Quartz: Brazil, Switzerland and the USA Rose Quartz: finest-quality are from Brazil, Other sources include India, Madagascar, and Sri Lanka. Rock Quartz: Brazil, Madagascar, Switzerland, and the United States Tiger's Eye: India, Sri Lanka, South Africa, Myanmar, and Western Australia Quartzite: India, Brazil, Russia, Tanzania MAIN SYNTHETIC PROCESS: Amethyst: hydrothermal method started in the 1970's with untwinned seed crystals, but in the 1990s, Chinese, Russian, and Japanese producing using twinned natural seed crystal Quartz: produced via the hydrothermal method resulting in untwinned quartz for use in the electronics industry, amethyst- citrine- ametrine have aslo been produced this way ( blue has also been produced) COMMON IMITATION MATERIAL: CUTTING/TRADING CENTER: Amethyst: cutting and marketing centers are in India, China, and Thailand, China produces most of the jewelry, marketing is mostly done on shopping networks GRADING: Amethyst Grade Terms: top grade "super", "extra", "AAA", "African", "Zambian", Calibrated Amethyst graded as “medium-dark,” “AA,” or “A", light desaturated purple, known in the trade as lilac are graded as "B" or medium, grayish to slightly grayish pale purple color are graded as "light" or "C"