Coral has been prized throughout history for its natural beauty. Like pearl, coral is also an biogenic gem consisting of more than 90% calcium carbonate. All coral consists of the remains of skeleton-like support structures that were built by colonies of very small marine animals, known as coral polyps. Proteinaceous coral differs from calcareous coral because it is made up of strong keratin proteins.
Cortez pearls come from the Gulf of California also known as the “Sea of Cortez”. The pearls are harvested from the Panamic Black-Lipped Oyster (Pinctada mazatlanica) and the Rainbow-Lipped mollusk (Pteria sterna). Only about 4,000 pearls harvested each year meet the industry’s quality standards to be sold on the gem market. The pearls have a beautiful luster due to their exceptional nacre thickness. The pearls can come in silver, gray, gold, green, blue, violet, purple, and black with pink, violet, blue and green overtones. The pearls average 6.5 to 8.5mm but some 14mm pearls are known.
Corundum is a mineral species best known for its two popular gemstone varieties, sapphire and ruby. All colors of corundum except red are known as sapphire. The term sapphire, when used without any modifiers, refers to only the blue variety of corundum. Red stones are known as ruby. Material that are not gemstones are simply known by the name corundum.
Creedite was discovered in the Colorado Fluorspar Co. Mine in 1916. The mine is located in the Creede Quadrangle, Mineral County, Colorado and this was the inspiration for its name. It comes in colorless, orange, purple, violet, and white prismatic crystals that sometime radiate from the base.
Crocoite was once called “Red Lead Ore” due to its lead content. The name Crocoite comes from "crocon" the Greek word saffron. Specimens are bright yellow, orange, or dark red and typically form as long prismatic crystals. Some of the best examples come from Australia.
Lead glass or crystal glass is frequently called crystal. George Ravenscroft patented a process for making lead crystal around 1673 in London. The addition of barium oxide, lead oxide, potassium oxide or zinc oxide, to glass improves clarity, raises the refractive index, and increases dispersion. Famous crystal manufacturing houses are located in Austria, France, Ireland, and Sweden.
Cubic Zirconia (abbreviated CZ) is the best-known man-made diamond simulant. A simulant is any material, natural or created by man, which imitates the appearance of a natural gem whereas a synthetic gem is man-made but must have a natural counterpart that duplicates the chemical, optical, and physical properties of the natural gem. While it's often touted as the most popular diamond simulant, cubic zirconia is also a synthetic gem. Natural crystals of cubic zirconia have only been found as inclusions in zircon.
Cuprite is a secondary mineral formed by the oxidation of copper sulfide veins. It is commonly found with native copper and malachite, and forms as both transparent red and lustrous, submetallic crystals. Transparent crystals may be faceted if large enough, but specimens are also commonly displayed as a glittering bed of crystals.
Danalite is a very rare brown, yellow to pink-red colored mineral named for the American mineralogist James Dwight Dana in 1866. Danalite has a limited number of global sources, including the New England states of Massachusetts, Rhode Island and Delaware.
In 1839 American mineralogist Charles Upham Shephard discovered a clear, bright, colorless gemstone in Danbury, Connecticut, and named it danburite after the location. Unfortunately for danburite, it was discovered at a time when colored gemstones were heavily promoted and highly desired. This colorless find, therefore, didn't create much excitement at that time. Danburite, which belongs to a class of minerals known as silicates, remained relatively unknown for years, but is steadily growing in popularity today.
Datolite is a phyllo-borosilicate commonly forming as nodules in igneous rocks. Facet-grade material rarely yields gems larger than 10 carats, with most being significantly smaller. Colorless, transparent datolite gems can be found in several locations worldwide, but many come from Connecticut, Massachusetts, New Jersey, and Virginia. Copper-stained, opaque nodules from Michigan are typically fashioned into cabochons.
Demantoid garnet is one of the most desirable of all colored gemstones and extremely rare. A color variety of andradite garnet, the name demantoid originates from the old German word demant meaning "diamond-like," because of a luster and dispersion that yields a fire even higher than diamonds.
This type of opal features dendrites, which are fern-like inclusions of iron, manganese, or other metallic oxides that create bold patterns within the gem. Typically, dendritic opals are cut into slices to best exhibit nature's artwork. As you might guess, these pieces are one-of-a-kind, as no two dendritic patterns are the same. Usually these opals are white, yellow, blue, green, or pink and show black inclusions well.
Ahh, diamonds. Everyone knows what diamonds are, but most might not realize what they once were: chunks of dark, nondescript carbon similar to charcoal, roasting and rumbling around deep within the earth. Fortunately, through eruptions and other harsh works of Mother Nature, diamonds eventually find their way to the surface for man to find, cut, polish, and enjoy. Talk about an ugly duckling turning into a swan! Named from the Greek word adamas, meaning "unconquerable," diamonds are renowned for their impeccable hardness and stellar brilliance.
Diaspore is beautiful and exotic in a soft, subtle manner. It is also one of the lesser known of the color-change gemstones. Some of the finest examples of gem quality diaspore are found in Turkey's Anatolian Mountains, but it can be found in numerous places around the globe. A rising star in fine jewelry, it's easy to fall in love with its sparklingly brilliant, tranquil earthy colors.
Diopside can be colorless but it most often a bottle green, brownish green or light green. Bright green diopside is commonly known as chrome diopside because of its chromium content. A rare blue variety known as violan may be found in Italy.
Dioptase is a bright emerald-green or blue-green gemstone noted for the visibility of internal cleavage planes. The transparent to translucent dioptase gemstone is uncommon and generally found in desert regions. Rivaling the beauty of emerald, dioptase is typically sold as specimens and gemstones are rarely seen, especially in sizes over 1 carat.
Dolomite is a white to brownish and sometimes pink-colored mineral named for French mineralogist Dodat Gratet de Dolomieu in 1791. Specimens are usually found in crystal clusters and have been known to be large in size. Transparent dolomite gems can be difficult to find due to their cleavage and low hardness value. They are usually preferred as a collector’s stone.
The word "drusy," is a mineralogical term used as both a noun and an adjective. The noun refers to a mineral coating of thin layers of tiny, tightly-packed crystals that resemble glittering sugar granules. The adjective refers to any such granulated crystal layers in reference to a given mineral; in this case, drusy quartz. Drusy quartz is usually found in the inside of geodes. When fashioned into loose gemstones and jewelry, it is often coated with a metallic color to capitalize on the glittering natural crystal facets and give it a more bold appearance.
A mineral that often forms as an inclusion in quartz, dumortierite is usually fashioned as cabochons or beads for jewelry. While prized for its deep violet to blue colors, it may also be found in shades of pink, gray and brown. Named for French paleontologist Eugene Dumortier, dumortierite is an exotic gem that is durable, untreated, and rare.