Quartz Value, Price, and Jewelry Information

Comments by Don Clark, CSM IMG

Quartz is one of the most common minerals on earth. (See The X Factor.) It is well loved as amethyst, citrine, rose, and smoky quartz. There are many other natural varieties, plus synthetic quartz that comes in every color of the rainbow.

Rock crystal, colorless quartz, is rarely used as a gem. However, it is prized by carvers and frequently used as caps for triplets.

Amethyst ranges from a light, pinkish violet to an opaque purple. The lightest shades are called "Rose de France." While currently out of vogue, they have traditionally been very fashionable. Today, the variety most in demand is "Siberian." That does not refer to its origin, but to dark purple coloring, with flashes of red or blue.

Citrine is the yellow to orange variety of quartz. These are the colors traditionally associated with topaz, and they are still confused by many. Its color ranges from a light lemon yellow, to a rich orange. "Madeira" citrine is a strong orange color, with red flashes. It is created by heat treating citrine with the proper iron content and demands the highest price.

Relatively new on the market is ametrine, with zones of both purple and yellow. The colors only reach a medium level of saturation and are never very dark. Cutting the material so both color show is sometimes a challenge for the lapidary. However, a well cut, bi-colored gem is a real delight. Ametrine is only found in Bolivia.

Smoky quartz is also mistaken for topaz. It comes in every shade of brown, from a light tan to nearly black. "Chocolate citrine" is a pleasant brownish/yellow color. Smoky quartz is known for its large sizes. The person who wants a really big gem, without a really big budget, often ends up with one of these.

Rose quartz receives its coloring fromfibrous inclusions of a mineral similar to dumortierite. It is always a light to medium pink, but sometimes is influenced by amethyst and picks up a violet shade. Until the 1980s, when a new deposit was discovered in Madagascar, it was never found completely transparent. Indeed, one of its best uses is for star cabs and spheres.

Tyndall scattering is one of the rarest phenomena in gemology, but it is relatively common in Madagascar rose quartz. Tyndall scattering is where light is dispersed by fine particles and produces a blue color. This is the same as what happens when sunlight hits dust particles in the air and why the is sky blue. In rose quartz, you see both pink and blue in the same tone.

While these are the most common varieties, they in no way exhaust the range of crystalline quartz. With the addition of inclusions, the list is nearly endless. In addition, there are stars and cats eye gems in this rich family of gemstones.

Optics

o= 1.544; e= 1.553 (very constant). Uniaxial (+).

Comments by Dr. Joel Arem

Crystalline Quartz

Crystalline quartz is separated here from cryptocrystalline or microcrystalline quartz. The crystalline varieties are those that occur in distinct, visible crystals: amethyst, smoky quartz, citrine, rose quartz, and milky quartz. The color origins in crystalline quartz are complex and are only now beginning to be fully understood.

The stable form of quartz below a temperature of 573°C is known as a-quartz. Between 573° and 870° another silica mineral, tridymite, forms. At 1470°, tridymite undergoes a structural rearrangement, resulting in the appearance of a new silica type called cristobalite, which is isometric. Finally, at 1710°, cristobalite melts to an extremely viscous liquid. If this liquid is chilled quickly, a glass forms (silica glass) that has many useful properties but no regular internal structure.

Cristobalite has no gem significance but appears in some types of volcanic glass as white globules and crystals resembling snowflakes. These form as a result of rapid cooling from high temperature.

The colored, crystalline quartz varieties generally occur in pegmatitcs and veins, having been deposited from water solutions over a long period of time. As a result of slow crystal growth, many such crystals achieve great internal perfection and yield enormous pieces of faceting rough. The only color varieties that do not form such large crystals are amethyst and rose quartz.

• Rock Crystal Used in faceted gems, beads. carving, decorative objects, and lamps. The material is common and has little intrinsic value, except in very large, flawless pieces. There are many types of mineral inclusions known. Occurrence: Hot Springs, Arkansas; Herkimer, New York; Swiss Alps; Minas Gerais, Brazil; Japan; Madagascar; New South Wales, Australia; Upper Burma; Canada.
• Milky Quartz The milkiness is due to myriad tiny cavities and bubbles filled with CO₂ or water. Vein quartz is often white and frequently contains gold. This quartz is little used in gems, except cabs with milky quartz and yellow gold specks. Occurrence: California; Colorado.
• Brown Quartz The variety called smoky quartz is pale beige, tan, brown, or deep brown in color. Very dark brown material is known as either morion or cairngorm, the latter from the locality in the Cairngorm Mountains, Scotland. The color appears to be caused by natural radioactivity. Occurrence: Minas Gerais. Brazil; Scotland; Madagascar; Switzerland; Korea; California; North Carolina.
• Yellow Quartz This variety is known as citrine and ranges in color from pale yellow through yellow-orange to rich golden orange, to very dark orange. A deep brown color is produced by heating certain types of amethyst. The name is from the old French citrin meaning yellow, and the color is due to ferric iron. Occurrence: Minas Gerais, Brazil; Madagascar.
• Amethyst Amethyst is violet or purple quartz. The lightest color, a pale lilac shade, is known as Rose of France. The deepest color, especially with flashes of red against a purple background, is referred to as Siberian. The term today usually implies a color rather than 8 locality. The name amethyst is from the Greek amethystos, meaning not drunken because the Greeks believed imbibing from an amethyst cup would prevent intoxication. Occurrence; Brazil; Zambia; USSR; Namibia; Australia; Nigeria; India; Uruguay; Mexico: Arizona; North Carolina. Inclusions: Prismatic crystals and negative cavities, thumbprint marks, so-called rippled fractures, and twinning lines. Transparent green quartz is produced by heating certain types of amethyst.
• Amethyst-citrine This material, also known as ametrine, tryxtine, and so forth, was originally reported from Rio Grande do Sul, Brazil, but later was shown to occur in Bolivia. Cut gems display both violet and yellow colors, sometimes in a striking zonal pattern, corresponding to rhombohedral growth regions. Heat treatment of both natural and synthetic amethyst can produce similarly colored material, and such stones are indistinguishable from natural ones.
• Rose Quartz The color of rose quartz is due to fibrous inclusions of a mineral similar to dumortierite. The material is nearly always cloudy or translucent, rarely transparent. The color is pale pink to deep pink, rarely rose—red. It is mainly used in cabochons, carvings, and decorative objects. Microscopic rutile needles may create a star effect. Occurrence: Maine; South Dakota; New York; Brazil; Madagascar; India; Japan; Namibia; USSR.
• Quartzite A rock made up of tightly packed quartz grains, formed at high temperature and pressure, due to metamorphism. Sometimes it contains small crystals that reflect light, and this material is called aventurine. Usually the included crystals are green, chrome-rich mica called fuchsite. Other micas that may form aventurine include gray varieties or brown types (from Chile). The density is usually 2.64-2.69. Occurrence: Spain; USSR; India; Chile.
• Dumortierite Quartz A dense, deep blue to violet material made up of crystalline quartz colored by dumortierite, a complex borosilicate.

Cryptocrystalline Quartz

Cryptocrystalline quartz varieties are colored chiefly by mineral impurities in the growth environment, including oxides of Fe, Mn, Ti, Cr, Ni, and other elements. They form either as gelatinous masses that slowly dehydrate and crystallize or by deposition from slowly percolating ground waters, depositing silica over a long period of time. This latter type of deposition results in banding that is seen in certain types of agate. Deposition within a spherical cavity, such as a gas pocket in basalt or other volcanic rock, results in concentric banding also seen in agates.

Cryptocrystalline quartz varieties offer a huge diversity of patterns and colors. The most generally widespread of these materials is composed of tiny fibers of silica and is known as chalcedony. Names within the cryptocrystalline quartz family are generally based on colors and patterns. The solid-colored materials are mostly chalcedony stained by oxides and are referred to as jaspers. Banded varieties, or materials with moss-like inclusions, are known as agate.

• Chalcedony Unstained material often grayish blue, compact form of silica. Occurrence: India; USSR; Iceland; Mexico; California. A purple-colored chalcedony from Arizona has been marketed under the trade name damsonite. The material occurs in veins and blocks up to 1 m thick, with masses over 100 kg recovered. Properties are normal for chalcedony (R.l. = 1.54, S.G. = 2.61), and coloration appears to be the same as that for amethyst.
• Carnelian Translucent to semi-opaque, red, orange-red, or brownish chalcedony. The color is due to iron oxide. Almost any chalcedony can be turned red by heating in an oven since it contains finely disseminated iron compounds that are oxidized by heating. Occurrence: Brazil; Uruguay; Egypt; India.
• Sard Similar to carnelian, sard is more brownish in color and more opaque. Occurrence: Brazil; Uruguay. Plasma: Deep green; opaque due to densely packed actinolite crystals.
• Prase Green or yellowish green chalcedony.
• Bloodstone Also known as heliotrope, consists of dark green plasma with blood-red and orange spots of iron oxides. Occurrence: India; Brazil; Australia; United States.
• Onyx Banded black and white chalcedony.
• Sardonyx Banded onyx, with red and white layers. Chrysoprase: Translucent green chalcedony colored by nickel. May resemble fine jade. Occurrence: Western Australia (Yandramindra, Wingelina, Kalgoorlie); USSR: Brazil; California.
• Flint and Chert Opaque, dull gray, or whitish chalcedony, very compact and hard.

Patterned Chalcedony

• Agate Usually takes the form of colored layers or bands, flat or concentric. Also mossy or dendritic inclusions, sometimes creating the impression of landscapes, vegetation, and so forth. Banded agates have regular color layers and bright colors. The moss agates have mossy inclusions of mineral oxides. Scenic agates have inclusions that look like pictures of scenery, with lakes, shorelines, trees. and shrubs. Lace agate is banded with intricate swirls and loops. Fire agate has platy crystals of iron oxide layered with chalcedony, resulting in iridescence brought out by cutting and polishing. Shell agate is patterned by silicified shells in the rock. Turritella agate is composed mostly of shells and shell fragments of the gastropod Turritella and certain other species. Occurrence: Moss agates are from India; Scotland, and the northwestern United States. Scenic agates are from Yellowstone National Park, Wyoming and Montana. Banded agate is from Brazil, Uruguay, Madagascar, Mexico, and the United States. Lace agate is from Mexico,Arizona, and Namibia (blue). Fire agate is from Mexico.
• Jasper Usually a mass of tiny silica crystals pigmented by impurities. The colors may be very strong, especially shades of brown, yellow, red, and green. Jasper occurs worldwide. Orbicular jasper has spherules of banded agate in a jasper matrix. Scenic or picture jaspers have fanciful patterns that may resemble scenery, such as ocean waves, shores, and rolling hills. Occurrence: Oregon; Idaho; Utah; Montana; Wyoming.
• Chrysocolla in Quartz: A tough, siliceous material consisting of blue chrysocolla in fine particles disseminated in silica, to produce a rich blue, hard material that takes an excellent polish. Occurrence: Arizona; New Mexico: Mexico.
• Petrified Wood: Colorful agate that has replaced tree trunks and limbs; the woody structure is preserved in many cases and can be seen with a microscope. The colors may be very bright and strong. Occurrence: Arizona; New Mexico; California; Washington; Oregon; various European countries; many other localities.
• Dinosaur Bone: Silicified dinosaur bone! It has a lovely brownish color and interesting pattem. Occurrence: Colorado; Wyoming; Utah. Other colors include red, pink, blue, purple, green, orange, etc.

Stone Sizes

• Rock crystal reaches enormous size, as illustrated by the 12.75-inch diameter, 107-pound perfect sphere of flawless Burmese material in Smithsonian Institution (Washington, D.C). This is the largest fine crystal ball in the world. Faceted gems of thousands of carats have been cut, such as the 7000 carat stone in Smithsonian Institution (Washington, D.C) and the 625 carat star quartz from New Hampshire.
• Citrines in the thousands of carats are also known. Smithsonian Institution (Washington, D.C) has Brazilian stones of 2258, 1180, 783, 278, 265, and 217 carats, for example, and most large museums have similar baubles.
• Smoky quartz: is in the same size league as citrine, but larger stones get very dark and opaque. Smithsonian Institution (Washington, D.C): 4500 (California) and 1695 (Brazil), plus others.
• Rose quartz gems are seldom transparent, especially above 20-30 carats. Large spheres of rose quartz are milky at best.
• Amethyst is rare in very large, transparent masses. The fine gems at Smithsonian Institution (Washington, D.C) are exceptional, such as the 1362-carat Brazilian stone and the 202.5-carat stone from North Carolina.
• Quartzite and milky quartz are massive varieties available in large pieces.
• Chalcedony is usually nodular, but masses can be several pounds and many inches in diameter.
• Star quartz is a rarity, but especially noted in rose quartz. SI has a sphere of Brazilian star material weighing 625 carats.
• Chrysoprase nodules of 700 and 1470 kilos have been found near Kalgoorlie, Western Australia.

Names

The name quartz comes from the Greek, "krystallos," meaning ice. Amethyst also comes from a Greek word. "Amethystos," meaning "not drunk." It was believed one could drink all night and remain sober if they had an amethyst in their mouth. Citrine is from the French, "citrin," meaning yellow.

Quartz is an unusual mineral. It is stable below 573 degrees Centigrade, but between 573 and 870 degrees, tridymite, (another silica mineral,) forms. At 1470 degrees, tridymite undergoes a structural rearrangement and becomes cristobalite, which is isometric. At 1710 degrees, cristobalite melts to a viscous liquid. If cooled quickly, it forms silica glass with no internal structure.

Tridymite and cristobalite have no gem significance; except that the "snowflakes" sometimes found in obsidian are cristobalite.

Quartz grows in primarily in pegmatites, but is hydrothermal grown in laboratories. Quartz grows very large, with cut gems in the thousands of carats. The exceptions are amethyst, which rarely produces a clean gem of 100 carats, and rose quartz, which rarely exceeds 30 carats in a transparent gem. Translucent specimens can weigh several pounds.

Quartz is one of the first gems to be synthetically grown on a large scale. Major development was done during World War II, to supply crystals for radios. Today, our computer industry is based on synthetic quartz. Not that there is a shortage of natural crystals, but the synthetics are always clean and are less time consuming to trim into the necessary pieces.

Rock crystal is from the Greek krystallos, meaning ice, because the Greeks thought it was ice frozen forever hard by an unnatural frost created by the gods. Amethyst comes from the Greek amethystos, as mentioned. Citrine is in allusion to the color citron (yellow). Chalcedony is an ancient name, perhaps from Chalcedon, a seaport in Asia Minor. Agate is from the Greek achate, the name of a river in southwestern Sicily where the material was found. Onyx is from the Greek word for nail or claw. Sard is from Sardis, the ancient locality reputed to be the origin of the stone. Carnelian is from the Latin carnis (flesh), in allusion to the red color. Plasma is from the Greek for something molded or imitated because it was used for making intaglios. Prase is from the Greek prason, meaning leek, in allusion to the color. Heliotrope is from Greek words helios (sun) and tropein (turn) because according to Pliny, it gives a red reflection when turned to face the sun while immersed in water. Flint and chert are of uncertain origin.

Enhancements

• Dying - changes or enhances color, requires quench crackling. Common, magnification shows dye concentrations. Some dyes fade, most stable.
• Foil back or coating - used on cabochons to enhance color and/or produce star. Occasional, detection is visible on surface. Stability depends on how stone is set, can be scratched off.
• Heat treatment - lightens smoky quartz and amethyst, turns some amethyst green, blue or yellow/orange. Occasional, undetectable, stability excellent.
• Irradiation - changes colors, common in smoky quartz, occasional in rose quartz. Undetectable, stability excellent.
• Quench crackling - creates fractures for iridescent effects, or to allow dye to penetrate. Occasional, undetectable, weakens stone.

Identifying Characteristics

Natural quartz, Color zoning, twinning, liquid, 2 and 3 phase inclusions, negative crystals, zebra stripes. May show bull's-eye or Airy's spiral.

Synthetic quartz is identified "breadcrumbs" or by a lack of natural inclusions. May also show 2-phase spicule inclusions or a seed. Cobalt blue, greenish yellow and grayish green, not found in nature.

Polariscope testing is no longer relevant, as some synthetics now duplicate natural twinning.

Variety and Trade Names

• Amethyst violet to purple, opaque to transparent
• Ametrine single crystal or stone with zones of both yellow and purple. Also called, amethyst-citrine, citrine-amethyst, golden amethyst and trystine.
• Angel hair, quartz with fine, gold rutile inclusions
• Aventurine, translucent to opaque quartzite with aventurescence. Usually green, but also gray, yellow and brown.
• Cairngorm, smoky quartz
• Citrine, yellow to orange
• Dumoriteritequartz, translucent to opaque colored dark blue or violet by dumoriterite inclusions
• Enhydro, crystals with a cavity filled with water. Usually eye visible and with a moveable air bubble.
• Gold quartz, milky quartz with native gold inclusions
• Golden amethyst same as ametrine
• Iris quartz, displays iridescent fractures. Also called Rainbow quartz.
• Milky quartz, translucent to opaque white, sometimes light gray or with bluish cast
• Morion, nearly opaque black
• Prasiolite or praeseplote transparent green to yellowish green.
• Quartzite, coarse aggregate of tightly packed crystals. Translucent to opaque, assorted colors.
• Rainbow quartz, same as Iris quartz
• Rock crystal, colorless, transparent
• Rose quartz, pink, semitransparent to transparent
• Rutilated quartz, translucent to transparent with easily visible rutile inclusions
• Sagenitic quartz, have straight crystal inclusions, usually rutile, tourmaline, or actinolite
• Siberian amethyst, dark color and showing flashes of red or blue
• Smoky quartz, transparent, light to dark brown. Also called Cairngorm
• Star quartz, translucent, white, rose, or gray showing asterism. Also called Asteriated quartz
• Tourmalinated quartz, translucent to transparent with easily visible tourmaline inclusions
• Trystine same as ametrine
• Venus hair, quartz with fine, gold rutile inclusions

Misnomers

• California lapis, Dumortierite quartz
• Herkimer diamond, double terminated, colorless quartz crystals from Herkimer, New York
• Indian jade, green aventurine quartz
• Moonstone, semitransparent, milky quartz
• Smoky topaz, misnomer for smoky quartz
• Topaz or topaz quartz for citrine