MINERALOGY OF GALLERY JEWELRY
ABALONE/PAUA
Abalone, Paua and mother-of-pearl cabochons are made from the inner nacreous layer of saltwater mollusk shells. The nacre or mother-of-pearl is mainly calcium carbonate (in the form of the mineral aragonite) and an organic horn substance (conchiolin) which form in multiple microcrystalline, concentric layers. This is the same process that oysters employ to form pearls. The nacre is built up at the rate of about a millimeter a year but secretion ceases after a few years. The iridescent color (called orient) is caused by the interference of light reflected by overlapping platelets of aragonite and intervening films of conchiolin. The Paua shell comes from the mollusk Haliotis australis most common in New Zealand waters. The indigenous Maori people have inlayed paua in carvings for centuries. Many Abalone species (Haliotis sp.) occur in both Pacific and Atlantic U. S. waters. These are commonly called Blacks, Reds, or Pinks based on their predominate shell color. The dust of all nacre is toxic.
AMAZONITE
Another name for this mineral is Amazon Stone, so named because of abundant deposits in that part of Brazil. Amazonite is a mostly opaque, green feldspar. Color distribution is irregular with many specimens having zebra-like stripes. The white stripes are caused by albite intergrowths while a black stripe pattern often results from included hornblende. Chemically, Amazonite is a potassium aluminum silicate and, like all feldspars, has a Moh’s hardness of about 6 (midway between turquoise and agate in hardness). The feldspars are one of the most abundant rock forming minerals. The potassium feldspars are called Orthoclase feldspars of which Amazonite is the most colorful. Amazonite gets this distinctive green color from traces of sodium compounds. Although Orthoclase feldspar is very widespread worldwide, gem-quality Amazonite is found in relatively few locations. Material from the western hemisphere (Brazil and many locations in the United States such as California, Colorado, and Virginia) is often relatively soft and fractured. The best Amazonite comes form India, Madagascar, Namibia or Russia.
CALSILICA
This mineral first appeared in the jewelry trade in 2002. There has been much controversy because of its unnatural looking rainbow color – intense bands of every color in the rainbow. An October, 2004 article in Lapidary Journal stated that two independent laboratory analysis found traces of commercial dyes. The major company marketing the mineral (Colbaugh Processing) maintains the color is natural, only enhanced by stabilization with acrylic resins – the same process commonly used for tourquoise. Chemically, Calsilica is microcrystalline calcite bonded with the amorphous clay mineral allophane. The Lapidary Journal article reported only powdered carbonate rock and epoxy resins. This controversy is complicated by various imitations being marketed as “Rainbow Calsilica”. The Colbaugh material is mined in Chihauhua, Mexico. The company has released pictures of the mine showing fractures in volcanic rhyolite filled with colorful Calsilica. The Mohs hardness is only about four so the material is noticeably softer than turquoise. The cabochon surface is subject to scratching if handled roughly.
CHAROITE
This mineral was first discovered about 1949 in the Russian Siberian Murun Massive, northeast of Lake Baikal. It was not recognized as an independent mineral until 1978. The mining area occurs along the middle reaches of the Charo River. According to Bob Jones, editor of Rock and Gem, if Peter the Great had known about Charoite, all of it would most likely be in Moscow palaces today. He proclaimed that all below ground resources belonged to the Czar. More than 13 mineral inclusions are associated with the lilac to violet mineral: the most common are the black sprays of aegirine-augite, yellow streaks of canasite, prisms of orange tinaksite and circular pools of microline feldspar. Chemically, Charoite is a hydrous silicate of sodium, calcium and potassium. It has an overall hardness of 5 to 6 and will take a high polish depending on the fibrous nature of the specimen.
ROMAN COIN / OPAL / SUNSTONE GOLD PENDANT
This pendant starts with a 13.9 gram lost wax casting in 14 kt yellow gold. Accents are torch and cold fabricated with 16 gauge 14 kt gold wire and 30 gauge gold sheet. The centerpiece is an authentic, silver, Roman denarius. (Purchased from Jim Folds, POB 25, Southington, OH, 44470 who bought the coin from Littleton Coin Company.) Pictured on the coin is the youngest Roman emperor, Gordian III, who reigned from 238 to 244 A.D. He was raised to the rank of Caesar by the Roman Senate when he was only 13 years old upon the execution of the previous emperor by the Praetorian Guard. Gordian was himself assassinated by his own generals when he was only 19 years old. The upper gemstone is a 3 ct Ethiopian opal purchased from Khalil Ur Rehman (Khaliljewels@yahoo.com) at the Tucson Gem Show. The lower stone is a 1 ct, green, Oregon Sunstone purchased from and faceted by Don Miller, Salem, OR. Don personally dug the rough at the Dust Devil Sunstone Mine, Plush, Oregon.
SCOTTISH COINAGE
Coins were minted in Scotland from 1136 until the 1707 Act of Union with England and Wales. Before this period Roman coins were used and after 1707 the London mint served all of Great Britain. Scotland used the pence – shilling – pound system similar to England: 12 pence (12d) = 1 shilling (1s) and 20 shillings (20s) = 1 pound. Scottish coins generally display the year of minting after 1539. The monarchs of Scotland who issued coins are as follows: David I (1124-1153), Malcolm IV (1153-1165), William the Lion (1165-1214), Alexander II (1214-1249), Alexander III (1249-1286), John Baliol (1292-1296), Robert the Bruce (1306-1329), David II (1329 – 1371), Robert II (1371-1390), Robert III (1390-1406), James I (1406-1437), James II (1437-1460), James III (1460-1488), James IV (1488-1513), James V (1513-1542), Mary Queen of Scots (1542-1567), James VI (1567-1625), Charles I (1625-1649), Charles II (1649-1685), James VII (1685-1689), William and Mary (1689-1694), William II (1694-1702), Anne (1702-1714).
GASPEITE
This is a light green mineral formed from the oxidation of nickel-rich rock. It was named for its discovery location on the Gaspe Peninsula in Quebec, Canada. The only other occurrence is in Western Australia. Gaspeite has been known to scientists for about 40 years but only within the last few years has it been widely used in jewelry. Its recent popularity stems from the uniqueness of the pea green color – rare in nature. Chemically, Gaspeite is an anhydrous (water-free) nickel, magnesium, iron carbonate. It has a hardness on the Moh’s scale of about 5 – similar to Turquoise. Also in common with Turquoise, Gaspeite often has brown inclusions of the common mineral Limonite or other natural hydrous iron oxides.
Because both Turquoise and Gaspeite are in short supply (as are Sugilite and red corals) reconstituted material has been developed. This is natural stone which has been pulverized and mixed with up to 20% epoxy resins. Reconstituted minerals are reformed under high temperature and pressure to retain the hardness and luster of the unaltered stone. Natural appearing patterns of trace minerals can also be duplicated in reconstituted minerals.
JADE (NEPHRITE)
The name jade comes from the Spanish “piedra de ijada” meaning “hip stone” as it was considered protection against kidney disease. The gemstone has been known for at least 7000 years. Shades of green are most common but literally all other colors occur. In 1863 Jade was proved to be two minerals: Nephrite (basic calcium magnesium iron silicate; hardness 6 – 6 ½; density 3) and Jadeite (sodium aluminum silicate; hardness 6 ½ – 7; density 3.3). Nephrite (Greek for “kidney”) proved to be a dense, felt-like, fibrous aggregate of two other minerals: Actinolite (more iron than magnesium in its molecular structure) and Tremolite (magnesium rich and iron poor). Nephrite is tougher than Jadeite because of this interlocking aggregate and one of the most difficult gemstones to cut on a diamond saw. Nephrite tolerates high temperature polishing to cause a surface molecular “flow”. This creates a unique mirror finish. Jadeite is rare being restricted to Burma and minor deposits in China, Canada, Guatemala, California and Russia. Nephrite is more common; major deposits are in New Zealand, Australia, Brazil, China, Siberia, British Columbia, Alaska, California, and Wyoming.
JASPER
This mineral is usually considered a form of chalcedony (sub-microscopic crystalline silicon dioxide). Jasper has a more grainy structure, is more opaque, and has more irregular iron oxide induced color patterns than other chalcedony varieties such as agate, petrified wood, bloodstone, or carnelian. Jasper is like other quartz varieties in that it has a Mohs’ hardness of 7 and polishes beautifully. The name Jasper is derived from the Greek for “spotted stone”. The typical multicolored, striped, and flamed patterns develop because Jasper may contain up to 20% other minerals. Jasper can be grown together with agate (jaspagate), opal or fossilized material. Deposits occur all over the world and numerous varieties have been named. Banded jasper can be of almost any color combination but tends to separate along the layers. Basanite is a fine-grained, black jasper used as the base layer in built up cabochons called doublets and triplets. Scenic jasper such as Bruneau, Owyhee, Willow Creek, Biggs, and Poppy are examples of picture jaspers named for their source location. Moukaite is a pink to light red and cloudy jasper found in Australia.
LAPIS LAZULI
This is an Arabic word meaning “blue stone” but is actually the name of a rock composed of several minerals. The blue color comes from the mineral Lazurite (sodium calcium aluminum silicate with some sulfer) which makes up 25 to 40 percent of Lapis Lazuli rock. The balance is: Augite (dark colored silicate of calcium, magnesium, iron, and aluminum), Calcite (white colored calcium carbonate, one of the most common minerals), Diopside (grayish calcium magnesium silicate), Enstatite (brown-green magnesium silicate), mica (a group of sheet silicates of varied color), Hornblende (black complex of basic silicates), Nosean (bluish sulfated sodium aluminum silicate), sodalite (blue chloric sodium aluminum silicate), and/or Pyrite (“fool’s gold”). Obviously, variations among Lapis specimens can be huge. The deposits producing the finest, evenly blue material are located in the remote limestone mountains of Afghanistan. The major deposits in Chile and Russia have appreciable amounts of calcite and diopside. Lesser producers are Angola, Burma, Canada and Pakistan. Lapis Luzuli is somewhat soft (Mohs’ hardness 5 – 6) and is sensitive to temperature,
LARIMAR
This is a single-source, blue variety of Pectolite, a hydrous calcium sodium silicate. The mineral has a compact, fibrous nature with a Moh’s hardness of 5, about the same as turquoise. Blue Pectolite has been familiar to local people in the Barahona province of southwestern Dominican Republic for a hundred years. It is formed in volcanic basalt and porphyry rocks by a rare process which produces blue tubular chimneys. Larimar, as a gemstone, was discovered in 1974 by a Peace Corps volunteer, Norman Rilling, and Miguel Mendez. The vivid blue tubes of Larimar are found in steep, remote terrain a few miles from the Caribbean. The mineral’s name is a combination of the first four letters of Mendez’ daughter’s name (LARIssa) and the Spanish word for sea (MAR). The discovery of the blue pipes by Rilling and Mendez was only possible because the two followed the path of eroded blue pebbles up the Barahona River. Larimar jewelry production has become a major economic venture in Dominican Republic. The Larimar Museum is a popular tourist attraction in the capital, Santo Domingo.
MALACHITE
The name is derived from the Greek “moloche”, the name of the mallow plant which shares the color of Malachite. It gets this distinctive dark green color from it’s significant copper content; it is a minor ore of copper. Malachite is a basic copper carbonate with a Mohs’ hardness of 3 ½ – 4. This softness and porous carbonate nature cause the mineral to be sensitive to heat and chemicals such as ammonia; the surface is easily scratched and sometimes becomes dull. Malachite develops as a secondary deposit in the zone of alteration around hydrothermal deposits. Massive nodules show the typical banding of light and dark green in concentric rings. Cabochons cut to expose these eye-like rings are called “peacock’s eye”. Azure-malachite is a striking blue and green variety from Arizona. Intergrowth of malachite, turquoise and chrysocolla results in the multi-colored Eilat stone from Israel. Republic of Congo is the most important Malachite producer. Other deposits are in Australia, Chile, Namibia, and Zimbabwe.
RHODOCHROSITE
The name Rhodochrosite is from the Greek “rhodon chros” for “rose colored”. It is a striped form of manganese carbonate which often contains calcium, iron, magnesium, and zinc – it is used as a manganese ore when available in large enough quantities. The Mohs’ hardness is only 3 ½ – 4 so cabochons often polish with a somewhat uneven sheen. Transparent forms are rare – the largest faceted crystal is 59 carats and is in a private collection in South Africa. Rhodochrosite has been on the market only since about 1940. The most common colors are raspberry red and pink but can be whitish, yellowish-brown, orange or gray and weathers to black. The most important deposits are near San Luis, Argentina where Rhodochrosite has formed as stalagmites in the silver mines of the Incas, abandoned since the 13th century. When cut in cross section these stalagmites display a concentric ring pattern and are called “Inca-rose”. Rhodochrosite deposits are widespread including Russia, Mexico, Namibia, Romania, South Africa, Spain as well as Colorado, Montana, Arkansas and Maine.
TURQUOISE
The name probably is derived from the French name for the country of Turkey which was an ancient trade route for the mines in Iran and Egypt. Turquoise has been mined in the southwestern United States by Native Americans since at least 200 BC. The largest known Turquoise nugget weighs 160 pounds, was found in 1926 in the Hachite Mountains of Arizona, and was sold in 2001 for $750,000. From 1891 until 1910 the Azure Company (a group of New York speculators) drove prices well above the price of gold. Most U.S. Turquoise mines have been exhausted and worldwide supply comes mostly from mainland China. The Chinese material has a distinctive greenish color often with inclusions of the brown mineral limonite. Small pieces of softer ore are commonly reconstituted or stabilized with epoxy resin. Chemically, the mineral is a hydrated phosphate of copper and aluminum. Hardness is between 5 and 6 therefore cabochons are often polished with paraffin.