Emerald

Emerald, the green variety of the mineral beryl, is the most famous and favored green gemstone. Its beautiful green color, combined with durability and rarity, make it one of the most valuable gemstones. Beryl also contains other, lesser known gem varieties, such as aquamarine and heliodor. Pure beryl is white; emerald's green color is caused by chromium impurities(and occasionally by vanadium impurities). Deep green is the most desired color in emeralds. The paler the color of the emerald, the lesser its value. Pale emeralds are not called emeralds, but "green beryl". They are sometimes heat-treated, in which they become aquamarine.

Emeralds are notorious for their flaws. Flawless stones are very uncommon, and are noted for their great value. Some people actually prefer an emerald with very minute flaws over a flawless emerald, as this proves authenticity of the stone. Many emerald flaws can be hidden by treating the emeralds with oil. Newer, more effective fracture-filling techniques are also practiced. Irradiation of some emerald gems is somewhat effective in removing certain flaws.

Many fakes and doublets are known. Two pale colored stones may be glued together with a deep green paste, creating a stone resembling emerald. Faceted green glass also resembles emerald, and it may be coated with a hard substance to mask its low hardness. Synthetic emeralds are also sold to unwary buyers without them knowing the stone is synthetic. Experts can distinguish all these fakes, and it is especially important to only purchase emeralds from reliable dealers. Experts can also determine if an emerald was treated with oil to mask internal flaws. Generally, unless otherwise specified, it can be assumed that an emerald has been treated with oil.

Chalcedhony

Chalcedony, also spelled Calcedony, is a very fine-grained (cryptocrystalline) variety of the silica mineral quartz It has a waxy luster and appears in a great variety of colors -- usually blue-white, buff, light tan, gray, yellow or brown.

A form of chert, it forms rounded crusts, rinds or stalactites (mineral deposits suspended from the roofs of caverns) in volcanic and sedimentary. It has a compact fibrous structure and fine splintery fracture. Other physical properties are those of quartz variously colored quartz with

In the petrified forests of the Desert Southwest, many of the original tree tissues have been replaced by chalcedony in the formation of petrified wood. What remains is a mineral replica of the original tree in various fantastic colors. The brilliant reds and greens are caused primarily by traces of iron oxides. Some of the best displays of petrified wood can be seen in eastern Arizona's Petrified Forest National Park.

In all ages many varieties of chalcedony have been used as gems and many colored varieties are still cut and polished as ornamental stones. Unless it is intricately carved or featured, Chalcedony is valued much less than it once was. Commercial production is primarily in Uruguay, Brazil and southwestern Africa.

It is said that chalcedony was used as a sacred by stones the Native Americas, promoting stability within the ceremonial activities of the tribe. Chalcedony is said to augment emotional balance, vitality, stamina, endurance, kindness, charity and friendliness. It supposedly alleviates hostilities, irritability and melancholy.

Chalcedony occurs in many varieties and colors. If chalcedony is conspicuously color-banded, it may be called aqate and with other minerals it has various other names including:

Agate: This common semiprecious variety of chalcedony is conspicuously color-banded with other minerals in successive layers. It occurs in bands of varying color and transparency in cavities of eruptive rocks or ancient lava. Agates come in many varieties themselves, including the following:

Moss Agate: Also called Mocha Stone, this grayish to milky-white chalcedony contains dark-colored, dendritic branching forms that resemble ferns, moss, or other vegetation. These formations are caused by the inclusion of mainly manganese and iron oxides of inorganic origin. Most moss agates are found as fragments weathered from volcanic rocks and long used for ornamental purposes.

Onyx: This striped, semiprecious variety of agate has black and white alternating bands. Onyx is used in carved cameos and intaglios because its layers can be cut to show a color contrast between the design and the background. Onyx is one of the 12 stones mentioned in the Bible as adorning the breastplate of the high priests.

Bloodstone: Also called Heliotrope, this dark-green variety of chalcedony has nodules of bright-red jasper distributed throughout. Bloodstone was greatly prized in the Middle Ages and was used in sculptures representing flagellation and martyrdom.

Carnelian: Translucent red chalcedony is called Carnelian, which owes its red to color to hematite (iron oxide). It is a close relative of Sard, which is brown in color. The Greeks and Romans used carnelian in rings and signets.

Chrysoprase: This brittle, translucent form of chalcedony owes its bright, apple-green color to the inclusion of nickel silicates, but heating or prolonged exposure to sunlight causes the color to fade.

Plasma: This semi-translucent, microgranular variety of chalcedony occurs in various shades of green, caused by amphibole or chlorite inclusions. Plasma often has nodules of gray quartz or Bloodstone throughout its mass. It has long been used for carvings and mosaics.

Camren Lucia Ruby

The Smithsonian's National Museum of Natural History has received one of the world's largest and finest ruby gemstones. The spectacular 23.1-carat Burmese ruby, set in a platinum ring with diamonds, was donated by businessman and philanthropist Peter Buck in memory of his wife Carmen Lúcia. The Carmen Lúcia Ruby will be on view indefinitely in the museum's National Gem Collection, part of the Janet Annenberg Hooker Hall of Geology, Gems and Minerals.

This extraordinary gemstone displays a richly saturated homogenous red color combined with an exceptional degree of transparency. In addition to the pleasant shape, the finely proportioned cut provides many vivid red color reflections. The stone was mined from the fabled Mogok region of Burma in the 1930s. While sapphire, emerald and diamond gems weighing hundreds of carats exist, high quality Burmese rubies larger than 20 carats are exceedingly rare.

RUBY

Ruby is the red variety of corundum, the second hardest natural mineral known to mankind. The non-red variety of corundum is Sapphire. Sapphires are well known among the general public as being blue, but can be nearly any color. The red color in ruby is caused by trace amounts of the element chromium. The best shade of red for ruby is often given the name "pigeon blood red", but ruby can be any shade of red up to almost pink.

Oriented rutile crystal inclusions cause a six-rayed-star light effect (called asterism) to form the popular Star Ruby.

Rubies come from all over the world but good gemstones are found at Thailand, India, Madagascar, Zimbabwe, North Carolina in the U.S., Afghanistan, Pakistan, Sri Lanka, Kenya, Tanzania, Kampuchea, and perhaps most notably, Burma.

Rubies have a famous place in science - the first lasers were made from artificial ruby crystals. They still are used for this purpose although other materials offer improved efficiency. Some ruby crystals show the fluorescence (actually very short term phosphorescence) that makes a laser possible.

Sapphire

Sapphire is the non-red variety of corundum, the second hardest natural mineral known to mankind. The red variety of corundum is Ruby - all other colors are called sapphire. Sapphires are well known among the general public as being blue, but can be nearly any color, even colorless. White (or colorless but massive) sapphire would more properly be called corundum. The blue color is by far the most popular color for sapphire but orange-pink, golden, white, and even black have generated much interest in the gem trade. Oriented rutile crystal inclusions cause a six-pointed-star light effect (called asterism to form the popular Star Sapphire.
Many of the finest watches have crystal faces made of artificial sapphire - these are extremely durable and scratch resistant.
One interesting bit of trivia - sapphire is aluminum oxide, and aluminum is a highly reactive metal. Any freshly exposed surface of aluminum is quickly oxidized to corundum (sapphire), so it can be said that your lawn chair (or screen door, or any other aluminum object) is coated with sapphire.

HARDNESS

Diamond is the hardest natural material known to humankind; hardness is defined as resistance to scratching. Diamond has a hardness of 10 (hardest) on Mohs scale of mineral hardness. Diamond's hardness has been known since antiquity, and is the source of its name.

The hardest diamonds in the world are from the New England area in New South Wales, Australia. These diamonds are generally small, perfect to semiperfect octahedra, and are used to polish other diamonds. Their hardness is considered to be a product of the crystal growth form, which is single stage growth crystal. Most other diamonds show more evidence of multiple growth stages, which produce inclusions, flaws, and defect planes in the crystal lattice, all of which affect their hardness.

The hardness of diamonds contributes to its suitability as a gemstone. Because it can only be scratched by other diamonds, it maintains its polish extremely well. Unlike many other gems, it is well-suited to daily wear because of its resistance to scratching—perhaps contributing to its popularity as the preferred gem in an engagement ring or wedding ring, which are often worn every day.

Industrial use of diamonds has historically been associated with their hardness; this property makes diamond the ideal material for cutting and grinding tools. As the hardest known naturally-occurring material, diamond can be used to polish, cut, or wear away any material, including other diamonds. However, diamond is a poor choice for machining ferrous alloys at high speeds. At the high temperatures created by high speed machining, carbon is soluble in iron, leading to greatly increased wear on diamond tools as compared to other alternatives. Common industrial adaptations of this ability include diamond-tipped drill bits and saws, or use of diamond powder as an abrasive. Industrial-grade diamonds are either unsuitable for use as gems or synthetically produced, which lowers their value and makes their use economically feasible.

General

A diamond is a transparent crystal of tetrahedrally bonded carbon atoms and crystallizes into the face centered cubic diamond lattice structure. Diamonds have been adapted for many uses because of the material's exceptional physical characteristics. Most notable are its extreme hardness, its high dispersion index, and extremely high thermal conductivity (900 – 2320 W/m K), with a melting point of 3820 K (3547 °C / 6420 °F) and a boiling point of 5100 K (4827 °C / 8720 °F).^[5] Naturally occurring diamonds have a density ranging from 3.15 to 3.53 g/cm³, with very pure diamond typically extremely close to 3.52 g/cm³.